6. what is the function of program counter in 8085 ... · memory location or i/o device. io/m...
TRANSCRIPT
6. What is the function of program counter in 8085
microprocessor? (May-2013)
Program counter stores the address of the next instruction to be fetched. Thus it
is used as pointer to the instruction.
7. What is trap interrupt and its significance? (May-2012)
This interrupt is a non-maskable interrupt. It is unaffected by any mask or
interrupt enable. TRAP has the highest priority. TRAP interrupt is edge and level
triggered. This means that the TRAP must go high and remain high until it is
acknowledged. This avoids false triggering caused by noise and transients.
8. List the control and status signals of 8085 and mention its
need. (Dec-2012)
ALE (Address Latch Enable)
and (Read and Write)
IO/ , S0 S1
READY
9. Define the function of parity flag and zero flag in 8085. (May-2012)
Parity flag – Parity is defined by the number of one‟s present in the accumulator.
After an arithmetic or logical operation if the result has an even number of ones,
ie., even parity, the flag is set. If the parity is odd, flag is reset.
Zero flag – the zero flag sets if the result of operation in ALU is zero and flag
resets if result is non zero. The zero flag is also is also set if a certain register
content becomes zero following an increment or decrement operation of that
register.
10. To obtain a 320 ns clock, what should be the input clock frequency? What
is the frequency of clock signal at CLK OUT? (May-2014)
System clock frequency = 1/T = 1 / 320*10-9
= 3.125 MHz
Crystal clock frequency = 2* System clock frequency
= 2*3.125*106
= 6.25 MHz
The frequency of clock signal at CLK OUT= Crystal frequency/2
= 6.25/2
=3.125 MHz.
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11. List the five interrupts pins available in the 8085.
(May-2010)
The five interrupt pins are
TRAP, RST 7.5, RST 6.5, RST 5.5, INTR.
12. Specify the size of data, address, and memory word and memory capacity
of 8085 microprocessor. (May-2011)
Size of data bus = 8-bits Size
of memory word = 8-bits
Size of address bus = 16-bits
Memory capacity = 64 Kbytes
13. What is interrupt? (May-2006, May-2009)
Interrupt is an external signal that causes a microprocessor to jump to a specific
subroutine.
14. How performance of a microprocessor is measured in terms of MIPS?
(June-2007)
The performance of a microprocessor is measured in terms of MIPS (Million
instructions per Second).
MIPS rate = 1/(Average time required for the execution of instruction * 106)
15. What are the different machine cycles in 8085 microprocessor? (May-2008)
Opcode fetch, Memory read, Memory write, I/O read, I/O write, Interrupt
acknowledge, Bus idle.
PART B
1.Draw and explain the architecture of 8085 in detail. (Nov/Dec-2013)
Address Bus:
The address bus is a group of 16 lines generally identified as A0 to A15. The address
bus is unidirectional and bits flow in one direction-from the MPU to peripheral
devices.The MPU uses the address bus to identify a peripheral or a memory (216 =
65,536) locations
Data Bus:
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The data bus is a group of 8 lines used for data flow. These lines are bi-directional and
data flow in both directions between the MPU and memory and peripheral devices. The
MPU uses the data bus to transfer data. Control Bus:
The control bus carries synchronization signals and providing timing signals.The MPU
generates specific control signals for every operation it performs.These signals are used
to identify a device type with which the MPU wants to communicate. Registers of 8085:
The 8085 have six general-purpose registers to store 8-bit data during program execution.
These registers are identified as B, C, D, E, H, and L.They can be combined as
registerpairs-BC, DE, and HL-to perform some 16-bit operations.
Accumulator (A):
The accumulator is an 8-bit register that is part of the arithmetic/logic unit (ALU).This
register is used to store 8-bit data and to perform arithmetic and logical operations.The
result of an operation is stored in the accumulator. Flags:
The microprocessor uses the 5 flags for testing the data conditions.They are Zero (Z),
Carry (CY), Sign (S), Parity (P), and Auxiliary Carry (AC) flags.The flagsare set or reset
according to the result of an operation.The bit position for the flags in flag register is,
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Figure: Architecture of 8085 Microprocessor
1. Sign Flag (S): If D7 of the result is1, the sign flag is set. Otherwise it is
reset. D7 is reserved for indicating the sign;
If D7 is 1, the number will be viewed as negative number.
If D7 is 0, the number will be viewed as positive number.
2. Zero Flag (Z): If the result of arithmetic and logical operation is zero, then zero flag is
set. Otherwise it is reset.
3. Auxiliary Carry Flag (AC): If D3 generates any carry when doing any arithmetic and
logical operation, this flag is set. Otherwise it is reset.
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4. Parity Flag (P): If the result of arithmetic and logical operation contains even number
of 1's then this flag will be set and if it is odd number of 1's it will be reset.
5. Carry Flag (CY):If any arithmetic and logical operation result any carry then carry
flag is set otherwise it is reset.
Arithmetic and Logic Unit (ALU):
It is used to perform the arithmetic operations like addition,subtraction, multiplication,
division, increment and decrement and logical operations like AND,OR and EX-OR.
It receives the data from accumulator and registers.According to the result the flag
register was set or reset.
Program Counter (PC):
This 16-bit register sequencing the execution of instructions. The function of the
program counter is to point to the memory address of the next instruction to be
executed.When an opcode is being fetched, the program counter is incremented by one
to point to the next memory location.
Stack Pointer (SP):
The stack pointer is also a 16-bit register used as a memory pointer.It points to a
memory location in R/W memory, called the stack.The beginning of the stack is defined
by loading a 16-bit address in the stack pointer.
Temporary Register:
It is used to hold the data during the arithmetic and logical operations.
Instruction Register:
When an instruction is fetched from the memory, it is loaded in the instruction register.
Instruction Decoder:
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It gets the instruction from the instruction register and decodes the instruction. It
identifies the instruction to be performed.
Serial I/O Control:
It has two control signals named SID and SOD for serial data transmission.
Timing and Control unit :
It has three control signals ALE, RD (Active low) and WR (Active low) and three status
signals IO/M(Active low), S0 and S1.
ALE is used for provide control signal to synchronize the components of
microprocessor and timing for instruction to perform the operation.
RD (Active low) and WR (Active low) are used to indicate whether the operation is
eading the data from memory or writing the data into memory respectively.
IO/M(Active low) is used to indicate whether the operation is belongs to the memory
or peripherals.
2.Draw the signal (pin diagram) configuration of 8085 and explain the purpose of
each signals. (Dec-2012)
8085 is a 40 pin IC, DIP package. The signals from the pins can be grouped as
follows
Power supply and clock signals
Address bus
Data bus
Control and status signals
Interrupts and externally initiated signals
Serial I/O ports
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Direct Memory Access (DMA):
Fig:Pin Diagram of 8085 Microprocessor
Power supply and Clock frequency signals:
Vcc : + 5 volt power supply
Vss : Ground
X1, X2 : Crystal or R/C network or LC network connections to set the
frequency of internal clock generator.The frequency is internally divided by
8
two. Since the basic operating timing frequency is 3 MHz, a 6 MHz crystal is
connected externally.
CLK (OUT):Clock Output is used as the system clock for peripheral and
devices interfaced with the microprocessor.
Address Bus:A8 - A15 (Input)
It carries the most significant 8 bits of the memory address or the 8 bits of the I/O
address;
Multiplexed Address / Data Bus:AD0 - AD7 (Input/Output)
These multiplexed set of lines used to carry the lower order 8 bit address as well as
data bus.
During the opcode fetch operation, in the first clock cycle, the lines deliver the
lower order address A0 - A7.
In the subsequent IO / memory, read / write clock cycle the lines are used as
data bus.
The CPU may read or write out data through these lines.
Control and Status signals:
Control Signals:
ALE (output) - Address Latch Enable.
This signal helps to capture the lower order address presented on the
multiplexed address / data bus.
RD (output , active low) - Read
This indicates that the selected memory location or I/O device is to be read and
the data bus is ready for accepting data from the memory or I/O device.
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WR (output, active low) - Write
This indicates that the data on the data bus is to be written into the selected
memory location or I/O device.
IO/M (output) - Memory/ IO
This status signal indicates that the read / write operation relates to whether the
memory or I/O device.
It goes high to indicate an I/O operation.
It goes low for memory operations.
Status Signals:S1,S0
It is used to know the type of current operation of the microprocessor.
S1 S0 Operation Specified
0 0 Halt
0 1 Memory Or I/O Write
1 0 Memory Or I/O Read
1 1 Instruction Fetch
Interrupts and Externally initiated operations:
They are the signals initiated by an external device to request the microprocessor
to do a particular task or work.
There are five hardware interrupts called,
1. TRAP
2. RST 7.5
3. RST 6.5
4. RST 5.5
5. INTR
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TRAP interrupt is a nonmaskable restart interrupt. It is unaffected by any mask or
Interrupt Enable. It has the highest priority of any interrupt.
RESTART INTERRUPTS: These three inputs have the same timing as INTR. They
are RST 7.5,RST 6.5, RST 5.5
Types of Interrupts
Priority
TRAP
Highest
RST 7.5
RST 6.5
RST 5.5
INTR
Lowest
On receipt of an interrupt, the microprocessor acknowledges the interrupt by the
active low INTA (Interrupt Acknowledge) signal.
Reset In (input, active low)
This signal is used to reset the microprocessor.
The program counter inside the microprocessor is set to zero.
The buses are tri-stated.
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Fig:Signal Diagram of 8085 Miicroprocessor Reset Out (Output)
It indicates CPU is being reset.
Used to reset all the connected devices when the microprocessor is reset.
Serial I/O ports:
SID (input) - Serial Input Data
Serial input data line The data on this line is loaded into accumulator bit 7
whenever a RIM instruction is executed.
SOD (output) - Serial Output Data
The output SOD is set or reset as specified by the SIM instruction.
These signals are used for serial communication.
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Direct Memory Access (DMA):
HOLD :HOLD signal is generated by the DMA controller circuit. The I/O device
request the processor for the address/data bus for bulk data transfer.
HLDA:(HOLD ACKNOWLEDGE) On receipt of HOLD signal, the microprocessor
acknowledges the request by sending out HLDA signal and leaves out the control
of the buses. After the HLDA signal the DMA controller starts the direct transfer
of data.
READY (input)
Memory and I/O devices will have slower response compared to
microprocessors.
Before completing the present job such a slow peripheral may not be able to
handle further data or control signal from CPU.
The processor sets the READY signal after completing the present job to access
the data.
The microprocessor enters into WAIT state while the READY pin is disabled.
3.Explain the interrupt structure of 8085 microprocessor. (Nov/Dec-2013)
Interrupt is a signal send by an external device to the processor, to perform a
particular task or work. Mainly in the microprocessor based system the interrupts are
used for data transfer between the peripheral and the microprocessor. When a
peripheral is ready for data transfer, it interrupts the processor by sending an
appropriate signal to the interrupt pin of the processor. If the processor accepts the
interrupt then the processor suspends its current activity and executes an interrupt
service subroutine to complete the data transfer between the peripheral and processor.
After executing the interrupt service routine the processor resumes its current activity.
This type of data transfer scheme is called interrupt driven data transfer scheme.
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Types of Interrupts :
The interrupts are classified into software interrupts and hardware interrupts.
SOFTWARE INTERRUPTS:
The software interrupts are program instructions. These instructions are inserted at
desired locations in a program. While running a program, lf a software interrupt
instruction is encountered, then the processor executes an interrupt service routine
(ISR).
The software interrupts of 8085 are RST 0, RST 1, RST 2, RST 3, RST 4, RST 5,
RST6 and RST7.
All software interrupts of 8085 are vectored interrupts. The software interrupts cannot be
masked and they cannot be disabled. When the processor encounters the software
instruction, it pushes the content of PC to stack. Then loads the Vector address in PC
and starts executing the ISR stored in this vector address. At the end of ISR, a return
instruction – RET will be placed. When the RET instruction is executed, the processor
POP the content of stack to PC.
Interrupt Vector address
RST 0 0000H
RST 1 0008H
RST 2 0010H
RST 3 0018H
RST 4 0020H
RST 5 0028H
RST 6 0030H
RST 7 0038H
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HARDWARE INTERRUPTS:
The hardware interrupts are initiated by an external device by placing an appropriate
signal at the interrupt pin of the processor.The processor keeps on checking the
interrupt pins at the second T-state of last machine cycle of every instruction.If the
processor finds a valid interrupt signal and if the interrupt is unmasked and enabled,
then the processor accepts the interrupt.The acceptance of the interrupt is
acknowledged by sending an INTA signal to the interrupted device. The processor
saves the content of PC in stack and then loads the vector address of the interrupt in
PC.If the interrupt is non-vectored, then the interrupting device has to supply the
address of ISR when it receives INTA signal. It starts executing ISR in this address.At
the end of ISR, a return instruction, RET will be placed.When the processor executes
the RET instruction, it POP the content of top of stack to PC. Thus the processor control
returns to main program after servicing interrupt.
The hardware interrupts of 8085 are TRAP, RST 7.5, RST 6.5, RST 5.5 and INTR
Further the interrupts may be classified into VECTORED and NON-VECTORED
INTERRUPTS.
VECTORED INTERRUPT:
In vectored interrupts, the processor automatically branches to the specific address in
response to an interrupt.
The TRAP, RST 7.5, RST 6.5 and RST 5.5 are vectored interrupts.
The vector addresses of hardware interrupts are given in the table.
Interrupt Vector address
TRAP 0024H
RST 7.5 003CH
RST 6.5 0034H
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RST 5.5 002CH
NON-VECTORED INTERRUPT:
In non-vectored interrupts the interrupted device should give the address of the interrupt
service routine (ISR).
The INTR is a non-vectored interrupt.
When a device interrupts through INTR, it has to supply the address of ISR after
receiving interrupt acknowledge signal.
TRIGGERING EDGE OF 8085 INTERRUPTS:
The TRAP interrupt is edge and level sensitive.To initiate TRAP, the interrupt signal has
to make a low to high transition and then it has to remain high until the interrupt is
recognized.The RST 7.5 interrupt is positive edge sensitive. To initiate the RST 7.5, the
interrupt signal has to make a low to high transition and it need not remain high until it is
recognized.The RST 6.5, RST 5.5 and INTR are level sensitive interrupts.Hence for
these interrupts the interrupting signal should remain high, until it is recognized.
MASKABLE & NON-MASKABLE INETRRUPTS:
The hardware vectored interrupts are classified into
Maskable Interrupts.
Non-maskable Interrupts.
Non-maskable Interrupts:
The interrupts which cannot be disabled are called Non-maskable Interrupts.
TRAP is non-maskable interrupt.
Maskable Interrupts:
The interrupts which can be enabled or disabled are called Maskable Interrupts.
RST 7.5, RST 6.5, RST 5.5 and INTR are Maskable interrupt.
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Masking is preventing the interrupt from disturbing the main program.When an interrupt
is masked the processor will not accept the interrupt signal.The interrupts can be
masked by executing SIM instruction. (SIM - Set InterruptMask).The status of maskable
interrupts can be read into accumulator by executing RIM instruction (RIM - Read
Interrupt Mask).All the hardware interrupts, except TRAP are disabled, when the
processor is resetted.They can also be disabled by executing DI instruction. (Dl-Disable
Interrupt).When an interrupt is disabled, it will not be accepted by the processor.To
enable the disabled interrupt, the processor has to execute El instruction (El-Enable
Interrupt).
INTERRUPT PRIORITY:
The order in which the interrupt has to be serviced is called Interrupt Priority.The priority
order of the 8085 interrupt is
Interrupt Interrupt Priority
TRAP 1
RST 7.5 2
RST 6.5 3
RST 5.5 4
INTR 5
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IMPORTANT SUMMARY ABOUT INTERRUPTS:
S.No Interrupt Vector Triggering Edge Maskable / Interrupt
Type
Address Non-Maskable
Priority
1 TRAP 0024H Edge and level Non-Maskable 1
Sensitive
2 RST 7.5 003CH Positive Edge Sensitive Maskable 2
3 RST 6.5 0034H Level Sensitive Maskable 3
4 RST 5.5 002CH Level Sensitive Maskable 4
5 INTR Non- Level Sensitive Maskable 5
Vectored
4..Draw the timing diagram for Opcode Fetch machine cycle, Memory Read
machine cycle,MemoryWrite,I/O read machine cycle and I/O write machine Cycle.
(Nov/Dec-2014)
Instruction Cycle:
The time required to execute an instruction is called instruction cycle.
Machine Cycle
The time required to access the memory or input/output devices is called machine
cycle.
T-State
A portion of an operation carried out in one system clock period is called as T-state.The
machine cycle and instruction cycle takes multiple clock periods.
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Opcode Fetch Machine Cycle: Fig: Timing Diagram of 8085 Microprocessor
Opcode fetch cycle is part of any instruction execution. In this machine cycle 8085
fetches opcode of instruction. The following are the sequence of actions that are
performed by 8085 to fetch an opcode from memory. This machine cycle consists of 4
T-states.
8085 places 16-bit address from PC on to the address bus and issues ALE pulse in
first T-state (T1). This is used to de-multiplex the address and data bus. It also issues
IO/M‟ signal to „0‟. This indicates that processor is performing memory related
operation. In second T-state (T2) processor issues RD‟ control signal to memory.
This enables memory to put data present at the address location given in previous T-
state on to data bus. RD‟ control signal is active for two clock pulses.
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In T3 state memory places opcode on Data bus. Processor reads opcode present on
data bus and de-asserts RD‟ signal. Thus data bus goes into high impedance state.
In T4 state processor decodes instruction and necessary actions are performed.
Memory Read machine cycle:
This machine cycle is required when an operand is present in memory. This machine
cycle requires three T-states. The following are the sequence of actions performed by
microprocessor during this machine cycle.
In the first T-state (T1) 8085 places address on address bus and issues ALE signal.
And also IO/M‟ signal is made low, since it is memory related operation.
In the second T-state (T2), processor issues RD‟ control signal to memory. In
response to this memory places data on data bus.
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In the third T-state (T3), processor reads data from data bus, and de-asserts RD‟
signal.
Memory Write Machine cycle:
This machine cycle is required when the results of operation needs to store in memory.
This machine cycle requires three T-states. The following are sequence of actions
performed by processor in this machine cycle.
In first T-state (T1), 8085 processor places 16- bit address on address bus and issues
ALE signal. And also it makes IO/M‟ signal to low, indicating it is memory related
operation.
In second T-state (T2), processor places data to be written on data bus and asserts
WR‟ signal to the memory.
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In the third T-state (T3), memory stores the data and processor de-asserts WR‟
signal.
IO read machine cycle:
This machine cycle is required, when data needs to be read from an input device. This
machine cycle requires three T-states. The following are the sequence of actions
performed by processor during this machine cycle.
In the first T-state (T1) 8085 places port address(for IO mapped addresses port
address is 8-bit, but for memory mapped addresses IO device address is 16-bit, but
reading from such is performed by memory read machine cycle) on address bus and
issues ALE signal. And also IO/M‟ signal is made high, since it is IO related operation.
In the second T-state (T2), processor issues RD‟ control signal to IO peripheral.
In response to this input device places data on data bus.
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In the third T-state (T3), processor reads data from data bus, and de-asserts RD‟
signal.
IO write Machine cycle:
This machine cycle is required when data needs to be output to an output device. This
machine cycle requires three T-states. The following are the sequence of actions
performed by processor during this machine cycle.
In first T-state (T1), 8085 processor places 8-bit port address on address bus (for IO
mapped addresses port address is 8-bit, but for memory mapped addresses, IO device
address is 16-bit, but writing to such is performed by memory write machine cycle) and
issues ALE signal. And also it makes IO/M‟ signal to high, indicating it is IO related
operation.
In second T-state (T2), processor places data to be written on data bus and asserts
WR‟ signal to the peripheral.
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In the third T-state (T3), peripheral accepts the data and processor de-asserts
WR‟ signal.
5.Explain how the memory organization was done in 8085.
8085 has 16 bit address bus, hence it can access 216 no. of memory locations,
which is equal to 64KB memory. Memory is required to store program as well as data.
Since microprocessor doesn‟t have on-chip memory, we need to connect it
externally.So it requires addressing mechanism.
The following are the steps involved in interfacing memory with 8085 processor.
1. First decide the size of memory requires to be interfaced. Depending on
this we can say how many address lines are required for it. For example if you
want to interface 4KB (212) memory it requires 12 address lines. Remaining
address lines can be used in address decoding.
2. Depending on the size of memory required and given address range,
construct address decoding circuitry. This address decoding circuitry can be
implemented with NAND gates and/or decoders or using PAL.
3. Connect data bus of memory to processor data bus.
4. Generate the control signals required for memory using IO/M‟, WR‟, RD‟
signals of 8085 processor.
Example:
Interface 4KB memory to 8085 with starting address A000H.
1. 4KB memory requires 12 address lines for addressing as already
mentioned. But 8085 has 16 address lines. Hence four of address lines are used
for address decoding
2. Given that starting address for memory is A000H. So for 4KB memory
ending address becomes A000H+0FFFH (4KB) = AFFFH.
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A0-A11 address lines are directly connected to address bus of memory chip. A12-A15
are used for generating chip select signal for memory chip.
Address decoding circuit using 3X8 decoder:
A15 line is use for enabling 74x138 decoder chip. A12, A13, A14 lines are connected to
74X138 chip as inputs. When theses lines are 010 output should be „0‟. This is provided
at O2 pin of 74X138 chip.
Address decoding circuit using only NAND gates:
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A15, A14, A13, A12 inputs should be 1010, for enabling the chip. So the circuit for this
is as shown above.
Types of address decoding:
There are two types of address decoding mechanism, based on address lines used for
generating chip select signal.
1. Absolute decoding
2. Partial decoding
Absolute decoding:
All the higher order lines of microprocessor, left after using the required signals for
memory are completely used for generating chip select signal.This type of decoding is
called absolute decoding. Partial decoding:
Only some of the address lines of microprocessor left after using the required
signals for memory are used for generating chip select signal. Because of this multiple
address ranges will be formed. If total memory space is not required for the system
then, this type of address decoding can be used. The advantage of this technique is
fewer components are required for memory interfacing because of this board size
reduces and in turn cost reduces.
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UNIT-II PROGRAMMING OF 8085 PROCESSOR
PART - A
1. What is indexing? NOV/DEC 2012
Indexing technique allows programmer to point or refer the data stored in sequential
memory locations one by one.
2.What are the various types of 8085 instructions?
MAY/JUNE2013,NOV/DEC2011
1. Data transfer group – MOV A,B 2. Arithmetic group – ADD B 3. Logical group- ANA B 4. Branch group – JMP LABEL 5. Stack I/O and Machine Control group – PUSH,POP,HLT.
3. Explain the difference between a JMP instruction and CALL instruction.
MAY/JUNE2012
A JMP instruction permanently changes the program counter. A CALL instruction leaves information on the stack so that the original program
execution sequence can be resumed.
4. What is meant by lookup table? NOV/DEC 2014
A lookup table is an array that replaces runtime computation with a simpler array
indexing operation.The savings in terms of processing time can be significant, since
retrieving a value from memory is often faster than undergoing an expensive
computation or input/ouput operation.
5. Explain the functioning of CMP instructions? NOV/DEC 2015
This instruction subtracts the contents of the specified register from contents of
the accumulator and sets the condition flags as a result of the subtraction.
6. Mention the similarity and difference between compare and subtract
instructions. May/June 2014
The compare and subtract instructions both are subtract one operand from
another and sets the flag register accordingly.The subtract instruction stores the result
in the accumulator while the compare instruction does not store any result except flags.
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7. State the purpose and importance of NOP instruction. May/June 2014
The NOP instruction in CPU‟s is to insert a time delay.It may be useful to force
the CPU to wait for external (slower) devices to complete its work.
8. What are the different types of addressing modes?NOV/DEC 2013,MAY/JUNE
2012
The addressing modes specifies the location of the operand(data). The different
types are as follows 1. Immediate addressing 2. Register addressing 3. Direct addressing 4. Indirect addressing 5. Implicit addressing
9. Define stack and stack related instructions? MAY/JUNE
2013,NOV/DEC2012
The stack is a group of memory locations in the R/W memory that is used for the
temporary storage of binary information during the execution of the program. The stack
related instructions are PUSH and POP 10. State the function of given 8085 instructions:JP,JPE,JPO,JNZ
JP – Jump on positive
JPE- Jump on parity even
JPO- Jump on parity odd
JNZ-Jump if no zero
S=0
P=1
P=0
Z=0
11.What are subroutine?
Subroutine are group of instructions stored as a separate program in memory
and it is called from the main program whenever required.
12.What is a recursive procedures?
A recursive procedure is a procedure, which calls itself. Recursive procedures
are used to work with complex data structures called trees. If the procedure is called
with N=3,then the N is decremented by 1 after each procedure CALL and the procedure
is called until N=0.
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13. How to access subroutine with in the main program procedure? NOV/DEC
2013 i) Accessed by CALL & RET instruction ii)Machine code of instruction is put only once in the
memory iii)With procedures less memory is required iv)Parameters can be passed in registers, memory location or stack 14.What are the four instructions which control the interrupt structure of the
8085 microprocessor? DI(disable interrupts)
EI(enable interrupts)
RIM(read interrupt masks)
SIM(set interrupt masks)
15. How the microprocessor is synchronized with peripherals?
The timing and control unit synchronizes all the microprocessor operations with
clock and generates control signals necessary for communication between the
microprocessor and peripherals.
PART - B
1. What are the different addressing modes in 8085 microprocessor? Explain it
with an example? NOV/DEC 2015,NOV/DEC 2014,NOV/DEC 2012,MAY/JUNE 2012
MAY/JUNE 2011
Addressing mode specifies the location of operand(data).Every instruction of a
program has to operate on a data. The method of specifying the data to be operated by
the instruction is called Addressing. The 8085 has the following 5 different types of addressing.
1. Immediate Addressing
2. Direct Addressing
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3. Register Addressing
4. Register Indirect Addressing
5. Implied Addressing
1.Immediate Addressing :
In immediate addressing mode, the data is specified in the instruction itself. The data
will be a part of the program instruction.All instructions that have „I‟ in their mnemonics
are of Immediate addressing type.
Example: MVI A, 01H- Move the data 01H given in the instruction to A register.
2.Direct Addressing :
In direct addressing mode, the address of the data is specified in the instruction.The
data will be in memory. In this addressing mode, the program instructions and data can
be stored in different memory blocks. This type of addressing can be identified by 16-bit
address present in the instruction.
Example:LDA 4500H- Load the data available in memory location 4500H in A register.
3.Register Addressing :
In register addressing mode, the instruction specifies the name of the register in which
the data is available.This type of addressing can be identified by register names in the
instruction.
Example: MOV A, B -Move the content of B register to A register.
4.Register Indirect Addressing :
In register indirect addressing mode, the instruction specifies the name of the register in
which the address of the data is available. The data will be in memory and the address
will be in the register pair.
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This type of addressing can be identified by letter „M‟ present in the instruction.
Example: MOV A, M - The content of memory (data) addressed by HL pair is
moved to A register.
5.Implied Addressing :
In implied addressing mode, the instruction itself specifies the type of operation and
location of data to be operated. This type of instruction does not have any address,
register name, immediate data specified along with it.
Example:CMA - Complement the content of accumulator
2.Explain the Different types of instruction in 8085. NOV/DEC 2013,MAY/JUNE
2013,NOV/DEC 2012,MAY/JUNE 2012,MAY/JUNE 2011
An instruction is a command given to the microprocessor to perform specified operation
on a given data.The instruction set of a microprocessor is the collection of instructions
that the microprocessor is designed to execute.It is classified into
1. Data Transfer Instructions.
2. Arithmetic Instructions.
3. Logical Instructions.
4. Branching / Control Transfer Instructions.
5. Stack & I/O Machine Control Instructions.
1.DATA TRANSFER INSTRUCTIONS:
The data transfer instructions move the data between registers or between registers
and memory. It copies the data from source location to destination location.No flags will
be affected. MOVE INSTRUCTION:
MOV Rd, Rs
31
MOV M, Rs
MOV Rd, M
This instruction copies the contents of the source register into the destination register.
The contents of the source register are not altered.If one of the operands is a memory
location, its location is specified by the contents of the HL registers.
Example: MOV B, C - This instruction move the content of C register to B register.
MOV B, M -This instruction move the content of memory location pointed by HL
register to B register.
MOVE IMMEDIATE 8-BIT:
MVI Rd, data
MVI M, data
The 8-bit data is stored in the destination registeror memory.If the operand is a memory
location, its location is specified by the contents of the HL registers.
Example:MVI A,01 - The data 01 will move to A register.
MVI M, 01 – The data 01 will move to the memory location pointed by HL
registers.
LOAD ACCUMULATOR:
LDA 16-bit address
The contents of a memory location, specified by a16-bit address in the operand, are
copied to the accumulator. The contents of the source are not altered. This is a 3-byte
instruction, the second byte specifies the low-order address and the third byte specifies
the high-order address. Example: LDA 4000 –The content of memory location 4000 is loaded into A register.
STORE ACCUMULATOR:
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STA 16-bit address
The contents of the accumulator are copied into the memory location specified by the
operand.This is a 3-byte instruction, the second byte specifies the low-order address
and the third byte specifies the high-order address. Example: STA 4500–The content of A register is loaded into memory location 4500.
EXCHANGE:
XCHG
The contents of register H are exchanged with the contents of register D, and the
contents of register L are exchanged with the contents of register E.
Example: XCHG :This instruction exchange the content of H and L with D and E
2.ARITHMETIC INSTRUCTIONS:
The arithmetic instructions includes addition, subtraction ,increment and decrement
operations.
ADDITION:
ADD REGISTER OR MEMORY TO ACCUMULATOR
ADD Rs
ADD M
The contents of the operand (register or memory) are added to the contents of the
accumulator and the result is stored in the accumulator. If the operand is a memory
location, its location is specified by the contents of the HL registers. All flags are
modified to reflect the result of the addition.
Example: ADD B – The content of A register is added with the content of B register and
the result is stored in A register.
ADD M -The content of A register is added with the content of
memory location pointed by HL register and the result is stored in A register.
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ADD REGISTER TO ACCUMULATOR WITH CARRY: ADC R
ADC M
The contents of the operand (register or memory) and the Carry flag are added to the
contents of the accumulator and the result is stored in the accumulator.If the operand is
a memory location, its location is specified by the contents of the HLregisters. All flags
are modified to reflect the result of the addition.
Example: ADC B -The content of A register is added with the content of B register and
also Carry and the result is stored in A register.
ADC M - The content of A register is added with the content of memory location
pointed by HL register and also carry and the result is stored in A register.
ADD IMMEDIATE TO ACCUMULATOR
ADI 8-bit data
The 8-bit data (operand) is added to the contents of the accumulator and the result is
stored in the accumulator.All flags are modified to reflect the result of the addition.
Example: ADI 45 – The data 45H is immediately added with the content of A register
and result Is stored in A register.
SUBTRACTION:
SUBTRACT REGISTER OR MEMORY FROM ACCUMULATOR
SUBRs
SUB M
The contents of the operand (register or memory) are subtracted from the contents of
the accumulator and the result is stored in the accumulator.If the operand is a memory
location, its location is specified by the contents of the HLregisters.All flags are modified
to reflect the result of the subtraction.
Example: SUB B – The content of A register is subtracted with the content of B register
and the result is stored in A register.
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SUB M -The content of A register is subtracted with the content of memory
location pointed by HL register and the result is stored in A register.
SUBTRACT SOURCE AND BORROW FROM ACCUMULATOR :
SBB R
SBB M
The contents of the operand (register or memory ) and the Borrow flag are subtracted
from the contents of the accumulator and the result is placed in the accumulator. If the
operand is a memory location, its location is specified by the contents of the HL
registers.All flags are modified to reflect the result in accumulator.
Example: SBB B -The content of A register is subtracted with the content of B register
and also Borrow flag and the result is stored in A register.
SBB M - The content of A register is subtracted with the content of memory
location pointed by HL register and also Borrow and the result is stored in A register.
SUBTRACT IMMEDIATE FROM ACCUMULATOR:
SUI 8-bit data
The 8-bit data (operand) is subtracted from the contents of the accumulator and the
result is stored in the accumulator. All flags are modified to reflect the result of the
subtraction.
Example: SUI 45 -The data 45H is immediately subtracted with the content of A register
and Result is stored in A register.
INCREMENT REGISTER OR MEMORY
INR R
INR M
The contents of the designated (register or memory) are incremented by 1 and the
result is stored in the same place.If the operand is a memory location, its location is
specified by the contents of the HL registers.
35
Example:INR B – The content of B register is incremented by 1.
INR M – The content of memory location pointed by HL register is incremented by 1.
INCREMENT REGISTER PAIR:
INX R
The contents of the designated register pair are incremented by1 and the result is
stored in the same place.
Example: INX H – The HL register pair is incremented by 1 and showing the next
memory location.
DECREMENT REGISTER OR MEMORY
DCR R
DCR M
The contents of the designated (register or memory) are decremented by 1 and the
result is stored in the same place.If the operand is a memory location, its location is
specified by the contents of the HL registers. Example:DCR B – The content of B register is decremented by 1.
DCR M –The content of memory location pointed by HL register is decremented by 1.
DECREMENT REGISTER PAIR:
DCX R
The contents of the designated register pair are decremented by1 and the result is
stored in the same place.
Example: DCX H – The HL register pair is decremented by 1 and showing the previous
Memory location.
3.LOGICALINSTRUCTIONS:
The logical instructions includes AND,OR,XOR,Complement operations.
36
Logical AND :
Logical AND register or memory with accumulator
ANA R
ANA M
The contents of the accumulator are logically ANDed with the contents of the operand
(register or memory), and the result is placed in the accumulator.If the operand is a
memory location, its address is specified by the contents of HL registers.S, Z, P are
modified to reflect the result of the operation. CY is reset. AC is set.
Example: ANA B - The content of A register is ANDed with the content of B register
and the result is stored in A register.
ANA M - The content of A register is ANDed with the content of memory
location pointed by HL register and the result is stored A register.
LOGICAL AND IMMEDIATE WITH ACCUMULATOR
ANI 8-bit data
The contents of the accumulator are logically ANDed with the 8-bit data (operand) and
the result is placed in the accumulator.S, Z, P are modified to reflect the result of the
operation. CY is reset. AC is set.
Example: ANI 45 -The data 45H is immediately ANDed with the content of A register
and result is stored in A register.
EXCLUSIVE OR REGISTER OR MEMORY WITH ACCUMULATOR
XRA R
XRA M
The contents of the accumulator are Exclusive ORed with the contents of the operand
(register or memory), and the result is placed in the accumulator.If the operand is a
memory location, its address is specified by the contents of HL registers.
37
S, Z, P are modified to reflect the result of the operation. CY and AC are reset.
Example: XRA B -The content of A register is XORed with the content of B register and
the result is stored in A register.
XRA M -The content of A register is XORed with the content of memory
location pointed by HL register and the result is stored A register.
EXCLUSIVE OR IMMEDIATE WITH ACCUMULATOR
XRI 8-bit data
The contents of the accumulator are Exclusive ORed with the8-bit data (operand) and
the result is placed in the accumulator.S, Z, P are modified to reflect the result of the
operation. CY and AC are reset.
Example: XRI 45 -The data 45H is immediately XORed with the content of A register
and result is stored in A register.
LOGICAL OR REGISTER OR MEMORY WITH ACCUMULATOR
ORA R
ORA M
The contents of the accumulator are logically ORed with the contents of the operand
(register/memory), and the Result is placed in the accumulator.If the operand is a
memory location, its address is specified by the contents of HL registers.
S, Z, P are modified to reflect the result of the operation. CY and AC are reset.
Example: ORA B -The content of A register is ORed with the content of B register and
the result is stored in A register.
ORA M- The content of A register is ORed with the content of memory
location pointed by HL register and the result is stored A register.
LOGICAL OR IMMEDIATE WITH ACCUMULATOR:
38
ORI 8-bit data
The contents of the accumulator are logically ORed with the8-bit data (operand) and the
result is placed in the accumulator.S, Z, P are modified to reflect the result of the
operation. CY and AC are reset.
Example: ORI 45 - The data 45H is immediately ORed with the content of A register
and result is stored in A register.
COMPLEMENT ACCUMULATOR:
CMA
The contents of the accumulator are complemented.
No flags are affected.
Example: CMA
COMPLEMENT CARRY:
CMC
The Carry flag is complemented.No other flags are affected.
Example: CMC
SET CARRY :
STC
The Carry flag is set to 1.No other flags are affected.
Example: STC
4. BRANCHING (CONTROL TRANSFER)INSTRUCTIONS :
The branching instructions are used to change the execution order.They are divided into
conditional jump/call or unconditional jump/call.
39
JUMP UNCONDITIONALLY
JMP 16-bit address
The program sequence is transferred to the memory location specified by the 16-bit
address given in the operand.
Example: JMP 4000
JUMP CONDITIONALLY
The program sequence is transferred to the memory location specified by the 16- bit
address given in the operand based on the specified flag of the PSW.
Example:
OPCODE DESCRIPTION FLAG STATUS
JC Jump on Carry CY = 1
JNC Jump on no Carry CY = 0
JP Jump on Positive S = 0
JM Jump on Minus S = 1
JZ Jump on Zero Z =1
JNZ Jump on no Zero Z = 0
JPE Jump on parity even P = 1
JPO Jump on parity odd P = 0
40
UNCONDITIONAL SUBROUTINE CALL :
CALL 16-bit address
The program sequence is transferred to the memory location specified by the 16-bit
address given in the operand. Before the transfer, the address of the next instruction
after CALL the contents of the program counter is pushed onto the stack. Example: CALL 4000
CONDITIONAL SUBROUTINE CALL :
The program sequence is transferred to the memory location specified by the 16-bit
address given in the operand based on specified flag of the PSW. Before the transfer,
the address of the next instruction after the call the contents of the program counter is
pushed onto the stack.
Example: CZ 4000
OPCODE DESCRIPTION FLAG STATUS
CC Call on Carry CY = 1
CNC Call on no Carry CY = 0
CP Call on Positive S = 0
CM Call on Minus S = 1
CZ Call on Zero Z =1
CNZ Call on no Zero Z = 0
CPE Call on parity even P = 1
41
CPO Call on parity odd P = 0
UNCONDITIONALRETURN FROM SUBROUTINE:
RET
The program sequence is transferred from the subroutine to the calling program. The
two bytes from the top of the stackare copied into the program counter, and program
execution begins at the new address.
Example: RET
CONDITIONAL RETURN FROM SUBROUTINE:
The program sequence is transferred from the subroutine to the calling program based
on the specified flag of the PSW.The two bytes from the top of the stack are copied into
the program counter, and program execution begins at the new address.
Example: RZ
OPCODE DESCRIPTION FLAG STATUS
RC Return on Carry CY = 1
RNC Return on no Carry CY = 0
RP Return on Positive S = 0
RM Return on Minus S = 1
RZ Return on Zero Z =1
RNZ Return on no Zero Z = 0
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RPE Return on parity even P = 1
RPO Return on parity odd P = 0
5.STACK I/O,MACHINE CONTROL INSTRUCTIONS:
These instructions are used to manipulate the stack to perform the input /output and to
alter the internal control flags.Unless specified the flags are not affected.
STACK INSTRUCTION:
PUSH :
Example: PUSH PSW
The contents of register A and the contents of condition flags which form the PSW are
pushed onto the stack.
POP INSTRUCTION:
Example: POP PSW
The contents of register A and the contents of condition flags which form the PSW are
restored from the stack.
I/O INSTRUCTION :
IN port
The data placed on the 8 bit bidirectional data bus by the specified port is moved to
register A.
OUT port
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The contents of register A are placed on the 8 bit data bus is transferred to the specified
port.
MACHINE CONTROL INSTRUCTION:
EI
The interrupt system is enabled.
DI
The interrupt system is disabled.
NOP
No Operation is performed.No flags are affected.
HLT
The processor is stopped.No flags are affected.
3.Write an 8085 ALP to add, subtract, multiply and divide two 8 bit numbers
stored at consecutive memory locations. NOV/DEC 2015
8 BIT ADDITION:
ALGORITHM:
1. Initialize memory pointer to data location.
2. Get the first number from memory in accumulator.
3. Get the second number and add it to the accumulator.
4. Store the answer at another memory location.
44
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENT
4100 START MVI C, 00 Clear C reg.
4101
4102 LXI H, 4500 Initialize HL reg. to
4500
4103
4104
4105 MOV A, M Transfer first data to
accumulator
4106 INX H Increment HL reg. to point
next memory Location.
4107 ADD M Add first number to acc.
Content.
4108 JNC L1 Jump to location if result
does not yield carry. 4109
410A
410B INR C Increment C reg.
410C L1 INX H Increment HL reg. to point
next memory Location.
410D MOV M, A Transfer the result from acc.
to memory.
45
410E INX H Increment HL reg. to point
next memory Location.
410F MOV M, C Move carry to memory
4110 HLT Stop the program
8 BIT SUBTRACTION:
1. Initialize memory pointer to data location.
2. Get the first number from memory in accumulator.
3. Get the second number and subtract from the accumulator.
4. If the result yields a borrow, the content of the acc. is complemented and 01H is
added to it (2‟s complement). A register is cleared and the content of that reg. is
incremented in case there is a borrow. If there is no borrow the content of the
acc. is directly taken as the result.
5. Store the answer at next memory location.
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENT
4100 START MVI C, 00 Clear C reg.
4102
4102 LXI H, 4500 Initialize HL reg. to
4500 4103
4104
4105 MOV A, M Transferfirstdatato
46
accumulator
4106 INX H Increment HL reg. to point
next mem. Location.
4107 SUB M Subtract first number from
acc. Content.
4108 JNC L1 Jump to location if result does
not yield borrow. 4109
410A
410B INR C Increment C reg.
410C CMA Complement the Acc. Content
410D ADI 01H Add 01H to content of acc.
410E
410F L1 INX H Increment HL reg. to point
next mem. Location.
4110 MOV M, A Transfer the result from acc.
to memory.
4111 INX H Increment HL reg. to point
next mem. Location.
4112 MOV M, C Move carry to mem.
4113 HLT Stop the program
8 BIT MULTIPLICATION:
47
ALGORITHM:
LOGIC: Multiplication can be done by repeated addition.
1. Initialize memory pointer to data location.
2. Move multiplicand to a register.
3. Move the multiplier to another register.
4. Clear the accumulator.
5. Add multiplicand to accumulator
6. Decrement multiplier
7. Repeat step 5 till multiplier comes to zero.
8. The result, which is in the accumulator, is stored in a memory location.
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENT
4100 START LXI H, 4500 Initialize HL reg. to
4500
4101
4102
Transfer first data to reg. B 4103 MOV B, M
4104 INX H Increment HL reg. to point
next mem. Location.
4105 MVI A, 00H Clear the acc.
4106
4107 MVI C, 00H Clear C reg for carry
48
4108
4109 L1 ADD M Add multiplicand multiplier
times.
410A JNC NEXT Jump to NEXT if there is
no carry 410B
410C
410D INR C Increment C reg
410E NEXT DCR B Decrement B reg
410F JNZ L1 Jump to L1 if B is not zero.
4110
4111
4112 INX H Increment HL reg. to point
next mem. Location.
4113 MOV M, A Transfer the result from
acc. to memory.
4114 INX H Increment HL reg. to point
next mem. Location.
4115 MOV M, C Transfer the result from C
reg. to memory.
4116 HLT Stop the program
49
8 BIT DIVISION:
ALGORITHM:
LOGIC: Division is done using the method Repeated subtraction.
1. Load Divisor and Dividend
2. Subtract divisor from dividend
3. Count the number of times of subtraction which equals the quotient
4. Stop subtraction when the dividend is less than the divisor .The dividend now
becomes the remainder. Otherwise go to step 2.
5. stop the program execution.
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENTS
4100 MVI B,00 Clear B reg for quotient
4101
4102 LXI H,4500 Initialize HL reg. to
4500H 4103
4104
4105 MOV A,M Transfer dividend to acc.
4106 INX H Increment HL reg. to point
next mem. Location.
4107 LOOP SUB M Subtractdivisorfrom
dividend
50
4108 INR B Increment B reg
4109 JNC LOOP Jump to LOOP if result
does not yield borrow 410A
410B
410C ADD M Add divisor to acc.
410D DCR B Decrement B reg
410E INX H Increment HL reg. to point
next mem. Location.
410F MOV M,A Transfer the remainder
from acc. to memory.
4110 INX H Increment HL reg. to point
next mem. Location.
4111 MOV M,B Transfer the quotient from
B reg. to memory.
4112 HLT Stop the program
4.Write an 8085 ALP to find largest & smallest numbers. MAY/JUNE 2011
LARGEST NUMBER:
ALGORITHM:
1. Place all the elements of an array in the consecutive memory locations.
2. Fetch the first element from the memory location and load it in the accumulator.
51
3. Initialize a counter (register) with the total number of elements in an array.
4. Decrement the counter by 1.
5. Increment the memory pointer to point to the next element.
6. Compare the accumulator content with the memory content (next element).
7. If the accumulator content is smaller, then move the memory content (largest
element) to the accumulator. Else continue.
8. Decrement the counter by 1.
9. Repeat steps 5 to 8 until the counter reaches zero
10. Store the result (accumulator content) in the specified memory location.
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENTS
8001 LXI H,8100 Initialize HL reg. to
8100H
8002
8003
8004 MVI B,04 Initialize B reg with no.
of comparisons(n-1)
8005
8006 MOV A,M Transfer first data to acc.
8007 LOOP1 INX H Increment HL reg. to
point next memory
location
8008 CMP M Compare M & A
8009 JNC LOOP If A is greater than M
52
800A then go to loop
800B
800C MOV A,M Transfer data from M to
A reg
800D LOOP DCR B Decrement B reg
800E JNZ LOOP1 If B is not Zero go to
loop1 800F
8010
8011 STA 8105 Store the result in a
memory location. 8012
8013
8014 HLT Stop the program
SMALLEST NUMBER:
ALGORITHM:
1. Place all the elements of an array in the consecutive memory locations.
2. Fetch the first element from the memory location and load it in the accumulator.
3. Initialize a counter (register) with the total number of elements in an array.
4. Decrement the counter by 1.
5. Increment the memory pointer to point to the next element.
6. Compare the accumulator content with the memory content (next element).
7. If the accumulator content is smaller, then move the memory content (largest
element) to the accumulator. Else continue.
53
8. Decrement the counter by 1.
9. Repeat steps 5 to 8 until the counter reaches zero
10. Store the result (accumulator content) in the specified memory location.
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENTS
8001 LXI H,8100 Initialize HL reg. to
8100H 8002
8003
8004 MVI B,04 Initialize B reg with no. of
comparisons(n-1) 8005
8006 MOV A,M Transfer first data to acc.
8007 LOOP1 INX H Increment HL reg. to point
next memory location
8008 CMP M Compare M & A
8009 JC LOOP If A is lesser than M then
go to loop 800A
800B
800C MOV A,M Transfer data from M to A
reg
800D LOOP DCR B Decrement B reg
54
800E JNZ LOOP1 If B is not Zero go to loop1
800F
8010
8011 STA 8105 Store the result in a
memory location. 8012
8013
8014 HLT Stop the program
5.Write an 8085 ALP to arrange in ascending and descending order. MAY/JUNE
2013,MAY/JUNE 2012
Ascending Order:
ALGORITHM:
1. Get the numbers to be sorted from the memory locations.
2. Compare the first two numbers and if the first number is larger than second then
interchange the number. 3. If the first number is smaller, go to step 4
4. Repeat steps 2 and 3 until the numbers are in required order
PROGRAM:
ADDRESS LABEL MNEM ONICS OPERAND COMMENTS
8000 MVI B,04 Initialize B reg with
number of comparisons 8001
(n-1)
8002 LOOP 3 LXI H,8100 Initialize HL reg. to
55
8003 8100H
8004
8005 MVI C,04 Initialize C reg with no. of
comparisons(n-1) 8006
8007 LOOP2 MOV A,M Transfer first data to acc.
8008 INX H Increment HL reg. to point
next memory location
8009 CMP M Compare M & A
800A JC LOOP1 If A is less than M then go
to loop1 800B
800C
800D MOV D,M Transfer data from M to D
reg
800E MOV M,A Transfer data from acc to
M
800F DCX H Decrement HL pair
8010 MOV M,D Transfer data from D to M
8011 INX H Increment HL pair
8012 LOOP1 DCR C Decrement C reg
8013 JNZ LOOP2 If C is not zero go to loop2
8014
56
8015
8016 DCR B Decrement B reg
8017 JNZ LOOP3 If B is not Zero go to loop3
8018
8019
801A HLT Stop the program
DESCENDING ORDER
ALGORITHM:
1. Get the numbers to be sorted from the memory locations.
2. Compare the first two numbers and if the first number is smaller than second then
interchange the number. 3. If the first number is larger, go to step 4
4. Repeat steps 2 and 3 until the numbers are in required order
PROGRAM:
ADDRESS LABEL MNEMONICS OPERAND COMMENTS
8000 MVI B,04 Initialize B reg with
number of comparisons 8001
(n-1)
8002 LOOP 3 LXI H,8100 Initialize HL reg. to
8100H 8003
8004
8005 MVI C,04 Initialize C reg with no.
of comparisons(n-1) 8006
57
8007 LOOP2 MOV A,M Transfer first data to
acc.
8008 INX H Increment HL reg. to
point next memory
location
8009 CMP M Compare M & A
800A JNC LOOP1 If A is greater than M
then go to loop1
800B
800C
800D MOV D,M Transfer data from M to
D reg
800E MOV M,A Transfer data from acc
to M
800F DCX H Decrement HL pair
8010 MOV M,D Transfer data from D to
M
8011 INX H Increment HL pair
8012 LOOP1 DCR C Decrement C reg
8013 JNZ LOOP2 If C is not zero go to
loop2
8014
8015
8016 DCR B Decrement B reg
58
8017 JNZ LOOP3 If B is not Zero go to
loop3 8018
8019
801A HLT Stop the program
59
UNIT-III 8051 MICROCONTROLLER
PART - A
1. What is Microcontroller?
A device which contains the microprocessor with integrated peripherals like memory,
serial ports, parallel ports, timer/counter, interrupt controller, data acquisition interfaces
like ADC, DAC is called microcontroller. 2. List the features of 8051 microcontroller. (Nov/Dec 2014)
The features are single supply +5 volt operation using HMOS technology. 4096 bytes
program memory on chip (not on 8031), 128 data memory on chip, Four register banks,
Two multiple modes, 16-bit timer/counter, Extensive Boolean processing capabilities, 64
KB external RAM size 3. How is the Program memory organized in an 8051 Microcontroller?
In an 8051 based system the entire 64KB program memory can be external or 4 KB
is internal and the remaining 60 KB is external. This is decided by the logic level of
the signal
EA Pin. When EA pin is tied high (+Vcc or 5 V) the first 4 KB of program memory is
internal and the remaining 60 KB is external. When EA pin is tied low (GND or 0 V) the
internal ROM is ignored and the entire 64 KB is external.
4. List the alternative functions assigned to port 3 pins of 8051 microcontroller.
(May/June 2011)
Port 3 Alternative
pins function
P3.0 Received Data
P3.1 Transmission Data
P3.2 INT0
P3.3 INT1
P3.4 T0
P3.5 T1
P3.6 WR
P3.7 RD
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5. What is the role of DPTR in 8051 Microcontroller?
The Data Pointer (DPTR) is the 8051s only user-accessible 16-bit (2-byte) register. The
Accumulator, "R" registers, and "B" register are all 1-byte values. DPTR, as the name
suggests, is used to point to data. It is used by a number of commands which allow the
8051 to access external memory. When the 8051 accesses external memory it will
access the external memory at the address indicated by DPTR. While DPTR is most
often used to point to data in external memory, many programmers often take
advantage of the fact that it‟s the only true 16-bit register available. It is often used to
store 2-byte values which have nothing to do with memory locations.
6. Mention the size of DPTR and stack pointer in 8051 microcontroller.
The DPTR is 16 bit data Register and SP is 8 bit Register. 7. What is the need of Coprocessor?
The general-purpose processors such as 8086 or 8085 are not optimized to do
arithmetic manipulations, CRT display manipulation and word processing. Hence we go
for a coprocessor, which is capable of doing dedicated functions (Special Operations) to
increase the overall execution speed of larger systems.
8. Write the vector address and priority sequence of 8051 interrupts (Nov/Dec
2014)
Vector
The interrupts are : address
External interrupt 0 : IE0: 0003H
TF0:
Timer interrupt 0 : 000BH
External interrupt 1 : IE1: 0013H
Timer Interrupt 1 : TF1:001BH
Serial Interrupt Receive
interrupt : RI: 0023H
Transmit interrupt : TI: 0023H
9. What are the addressing modes of 8051 microcontroller? (Nov/Dec 2014)
The 8051 provides a total of five distinct addressing modes.
(1) Immediate (2) register (3) direct (4) register indirect (5) indexed
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10. Mention the purpose of PSEN andEA in 8051microcontroller. (May/June
2014)
PSEN: If external ROM is used for storing program then a logic zero (0) appears on it
every time the microcontroller reads a byte from memory.
EA : By applying logic zero to this pin, P2 and P3 are used for data and address
transmission with no regard to whether there is internal memory or not. It means that
even there is a program written to the microcontroller, it will not be executed. Instead,
the program written to external ROM will be executed. By applying logic one to the EA
pin, the microcontroller will use both memories, first internal then external (if exists).
11. List the interrupt sources in 8051 microcontroller. (May/June 2014) (Nov/Dec
2015)
8051 Microcontroller has 5 interrupts: (1) External interrupt 0 (2) External interrupt
1 (3) Timer0 overflow (4) Timer1 overflow (5) Transmission interrupt (TI)/ reception
interrupt (RI) (6) Reset.
12. What is the function of R registers in 8051 Microcontroller?
(May/June 2013)
The R registers are in a group of register banks denoted as bank 0 to bank 3. The R
registers of any bank can take value from 0 to 7. At any one time the controller can use
any one of the register banks as general purpose registers. The selection of register
banks depends on the value of the bits RS0 and RS1 in the PSW registers. After a reset
the PSW register is cleared and so the controller works with register bank0. 13. Give the details of PSW of 8051. (May/June 2010)
The PSW stores the status of the results of the ALU operations and some of the status
of the processor by means of 1 bit status flags. The PSW is also known as flag register.
The flags are useful for the programmer to test condition of the result and make
decisions. The PSW consists of four math flags and two register bank select bits. The
Math flag are carry, auxiliary carry, overflow and parity flag. The register bank select bits
are RS0 and RS1.
14. Mention the registers used for serial communication in 8051 Microcontroller?
(Nov/Dec 2014)
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SCON- Serial port control register, SBUF- Serial port data buffer are the registers used
for serial communication in 8051 Microcontrollers.
15. Explain relative addressing in an 8051.
In relative addressing, the instruction specifies the address relative to the PC(Program
Counter). The instruction will carry an offset whose range is -12810 to +12710. The
offset is added to the PC to generate the 16 bit physical address.
Example: JC offset- If carry is one, then the program control jumps to an address
obtained by adding the content of the PC and the offset value in the instruction.
16. List the instructions that affect the overflow flag in 8051.
ADD, ADDC, SUBB, DIV and MUL. 17. Write the functions of TMOD register in 8051
Microcontroller. (Nov/Dec 2015) (MSB)
(LSB)
GATE C/T M1 M0 GATE C/T M1 M0
TIMER 1 TIMER 0
GATE- When GATE =1 hardware control GATE =0, software control
- Set 0 for Timer operation and Set 1 for Counter operation
M1 M0- Mode selector bit
0 0 - 13 bit timer
0 1 - 16 bit timer / counter 1 0 - 8 bit auto-reload timer /counter
1 1 - TL 0 is an 8 bit timer /counter controlled by standard timer 0 control bits. TH0 is
an 8 bit timer controlled by timer 1 control bits 18. What are the differences between a Microcontroller and Microprocessor?
Microprocessor Microcontroller
It is termed as general purpose
digital It is termed as special purpose digital
computer. Controller.
It contains the CPU, memory It possesses all features o
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addressing microprocessor
and additionally it includes timers
circuits and interrupt handling circuit. parallel
and serial I/O and the internal RAM and
ROM.
It has one or two types of bi
handling It has many bit handling instructions.
Instructions.
Memory and I/O access time is large. Memory and I/O access time is less.
PART - B
1. Explain with a neat block diagram the architecture of 8051microcontroller.
(May/June 2013) (May/June 2015)
The 8051 microcontroller is an 8-bit microcontroller.The major components of
8051microcontroller and their functions
1.ALU(ArithmeticandLogicUnit)
2.PC(ProgramCounter)
3.Registers
4.Timersandcounters
5.InternalRAMandROM
6.Fourparallelinput/outputports
7.Interruptcontrollogicwithfivesourcesofinterrupt
8.Serialdatacommunication
9.PSW(ProgramStatusWord)
10.DataPointer(DPTR)
11StackPointer(SP)
12.Address and Data bus.
13.Clock Circuits.
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Fig:Architecture of 8051 Microcontroller
1. Arithmetic and Logic Unit (ALU):
All arithmetic and logical functions are carried out by the ALU.
Addition, subtraction with carry, and multiplication come under arithmetic operations.
Logical AND, OR and EXOR come under logical operations.
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2.ProgramCounter(PC):
A program counter is a 16-bit register and it has no internal address.The basic function
of program counter is to fetch the next instruction to be executed.The PC increments
automatically, holding the address of the next instruction.
3.Registers:
Registers are usually known as data storage devices. 8051 microcontroller has 2
registers, namely Register A and Register B.These registers are used to store the
output of mathematical and logical instructions.
Accumulator(A Register):
A Register serves as an accumulator.The operations of addition, subtraction,
multiplication and division are carried out by A Register A Register is also involved in
data transfers between the microcontroller and external memory.
B Register:
Register B functions as a general purpose register. Register B is usually unused and
comes into picture only when multiplication and division functions are carried out by
Register A.
4. Timers and Counters :
Microcontroller 8051 has TWO 16 bit timers and counters.
The two timers are Timer0 and Timer1.
The two timers are divided into TH0 (8bit)TL0(8bit) and TH1(8bit)TL1(8bit).
5. Internal RAM and ROM:
ROM
The 8051 has a memory of 4KB on-chip ROM.
The 8051 ROM is a non-volatile memory.
It is also called as program memory.
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RAM
The 8051 microcontroller is composed of 128 bytes of internal RAM. This is a volatile
memory since its contents will be lost if power is switched off. These 128 bytes of
internal RAM are divided into 32 working registers.This 32 working registers divided into
4 register banks (Bank 0-Bank 3) with each bank consisting of 8 registers (R0 - R7).
There are 128 addressable bits in the internal RAM.It is also called as program memory.
6.FourParallelInput/OutputPorts:
The 8051 microcontroller has four 8-bit input/output ports. These are: P0,P1,P2,P3.
PORT P0:
When there is no external memory present, this port acts as a general purpose
input/output port.In the presence of external memory, it functions as a multiplexed
address and data bus. It performs dual functions.
PORT P1:
This port is used for various interfacing activities.This 8-bit port is a normal I/O port.
PORT P2:
This port can be used as a general purpose port when there is no external memory.
When external memory is present it works in conjunction with PORT PO as an address
bus.
.
PORT P3:
PORT P3 behaves as a dedicated I/O port.
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.InterruptControl:
A signal which is used to suspend or halt the normal program execution for a
temporary period of time in order to serve the request of another program or hardware
device is called an interrupt. An interrupt can either be an internal or external.
There are two ways of giving interrupts to a microcontroller
sending software instructions
sending hardware signals.
The interrupt mechanism keeps the normal program execution in a "put on hold" mode
and executes a subroutine program and after the subroutine is executed, it gets back to
its normal program execution.
In8051,5sourcesofinterruptsareprovided.Theyare:
a)2ExternalinterruptsourcesINT0andINT1
b) 3 Internal interrupt sources - Serial port interrupt, Timer Flag 0 and Timer Flag 1.
8. Serial Data Communication :
A method of establishing communication among computers is by transmitting and
receiving data bits is a serial connection network.The SBUF(Serial Buffer) register holds
the data.The SBUF register has 2 parts – one for storing the data to be transmitted
(done using TXD pin) and another for receiving data (done using RXD pin)from outer
sources.
The SCON (Serial Control) register manages the data communication.The PCON
(Power Control) register manages the data transfer rates.Two pins - RXD and TXD,
establish the serial network.There are 4 programmable modes in serial data communication. They are:
1.SerialDatamode0(shiftregistermode)
2.SerialDatamode1(standardUART)
3.SerialDatamode2(multiprocessormode)
4. Serial Data mode 3
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9.PSW(ProgramStatusWord):
Program Status Word is a register which holds a program's information and also
monitors the status of the program currently being executed.
PSW also has a pointer which points towards the address of the next instruction to be
executed.
CY AC RS1 RS0 OV Reserved P 0
CY – Carry
AC – Auxiliary Carry
RS1, RS0 – 00 Register bank 0
01 Register bank 1
10 Register bank 2
11 Register bank 3
OV – Overflow
P – Parity
10.DataPointer(DPTR):
The data pointer or DPTR is a 16-bit register. It is made up of two 8-bit registers called
DPH and DPL. Separate addresses are assigned to each of DPH and DPL. These 8-
bit registers are used for the storing the memory address.
11.StackPointer(SP):
The stack pointer (SP) in 8051 is an 8-bit register. The main purpose of SP is to
access the stack. Stack is a special area of data in memory. The SP acts as a pointer
for an address that points to the top of the stack.
12.DataandAddressBus:
A bus is group of wires using which data transfer takes place from one location to
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another within a system There are mainly two kinds of buses - Data Bus and Address
Bus
Data Bus:
The purpose of data bus is to transfer data. The no of data lines decides the word
length of the microcontroller. The data bus is bidirectional.
Address Bus:
The purpose of address bus is to transfer information. The information tells from where
within the components, the data should be sent to or received from. The no of address
lines decides the capacity of memory address. The address bus is unidirectional.
13.Clock Circuits:
Internal operations can be synchronized using clock circuits which produce clock
pulses.
With each clock pulse, a particular function will be done and hence synchronization is
achieved. There are two pins XTAL1 and XTAL2 which form an oscillator circuit which
connect to a resonant network in the microcontroller.Quartz crystal is used to generate
Clock pulse.
1. ALE(Address Latch Enable)Latches the address signals on Port P0
2. EA (External Address) - Holds the 4K bytes of program memory
3. PSEN (Program Store Enable) - Reads external program memory
4. RST (Reset) - Reset the ports and internal registers upon start up
2. Explain the interrupt structure of 8051 microcontroller. (May/June 2015)
An interrupt is a signal which interrupts normal program execution. Program flow
is always sequential, being altered only by those instructions and cause program flow to
deviate. Interrupts give to "put on hold" the normal program flow, and execute a
subroutine. After completion of subroutine microcontroller resume normal program flow.
This subroutine, called an ISR, which is only executed when a certain interrupt occurs.
The microcontroller 8051 has the following interrupt signals
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External 0 Interrupt
Timer 0 over flow Interrupt
External 1 Interrupt
Timer 1 over flow Interrupt
Serial Interrupt
The various interrupts and their different code depending on interrupt was executed.
This is done by jumping to a fixed address when a given interrupt occurs.
Types of Interrupts Interrupt Flag Interrupt Address
External 0 Interrupt IE0 0003H
Timer 0 over flow Interrupt TF0 000BH
External 1 Interrupt IE1 0013H
Timer 1 over flow Interrupt TF1 001BH
Serial Interrupt RI/TI 0023H
Whenever Timer 0 overflows (i.e., the TF0 bit is set), the main program will be
temporarily suspended and control will jump to 000BH.The program code at address
000BH that handles the interrupt of Timer 0 overflowing.
Interrupt Enable Register (IE Register):
All interrupts can be able to enable or disable.
D7 D6 D5 D4 D3 D2 D1 D0
EA X X ES ET1 EX1 ET0 EX0
D7 - EA- 1 - Enable all interrupts. 0-Disable all interrupts.
D4 - ES- 1 - Enable Serial port interrupt. 0- Disable Serial port interrupt.
D3 - ET1- 1- Enable Timer1 overflow interrupt. 0 – Disable Timer1 overflow interrupt.
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D2 - EX1- 1-Enable external interrupt1. 0 – Disable external interrupt1
D1 - ET0- 1-Enable Timer0 overflow interrupt. 0 – Disable Timer0 overflow interrupt
D0 - EX0-1-Enable External interrupt0. 0 – Disable External interrupt0.
or example, if you wish to enable Timer 1 Interrupt, you would execute either:
Polling Sequence:
The 8051 automatically evaluates whether an interrupt should occur after every
instruction. When checking for interrupt conditions, it checks them in the following order:
External 0 Interrupt
Timer 0 Interrupt
External 1 Interrupt
Timer 1 Interrupt
Serial Interrupt
This means that if a Serial Interrupt occurs at the exact same instant that an External 0
Interrupt occurs, the External 0 Interrupt will be executed first and the Serial Interrupt
will be executed once the External 0 Interrupt has completed.
Interrupt Priorities :
The 8051 offers two levels of interrupt priority: high and low. By using interrupt priorities
you may assign higher priority to certain interrupt conditions.Interrupt priorities are
controlled by the IP SFR (B8h).
Interrupt Priority Register (IP Register):
D7 D6 D5 D4 D3 D2 D1 D0
* * * PS PT1 PX1 PT0 PX0
The rules for interrupt priorities:
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Nothing can interrupt a high-priority interrupt--not even another high priority interrupt.
A high-priority interrupt may interrupt a low-priority interrupt.
A low-priority interrupt may only occur if no other interrupt is already executing.
If two interrupts occur at the same time, the interrupt with higher priority will execute first. If both interrupts are of the same priority the interrupt which is serviced first by polling sequence will be executed first.
Interrupt Signal Performance:
When an interrupt is triggered, the following actions are taken automatically by the
microcontroller
The current Program Counter is saved on the stack, low-byte first.
Interrupts of the same and lower priority are blocked.
In the case of Timer and External interrupts, the corresponding interrupt flag is cleared.
Program execution transfers to the corresponding interrupt handler vector
address.
The Interrupt Handler Routine executes.
If the interrupt being handled is a Timer or External interrupt, the microcontroller
automatically clears the interrupt flag before passing control to your interrupt handler
routine.
End of Interrupt:
An interrupt ends when the program executes the RETI (Return from Interrupt)
instruction. When the RETI instruction is executed the following actions are taken by the
microcontroller:
Two bytes are popped off the stack into the Program Counter to restore normal program execution.
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Interrupt status is restored to its pre-interrupt status.
Serial Interrupts :
Serial Interrupts are slightly different than the rest of the interrupts. There are two
interrupt flags: RI and TI. If either flag is set, a serial interrupt is triggered. In the serial
port, the RI bit is set when a byte is received by the serial port and the TI bit is set when
a byte has been sent. The serial interrupt is executed, because the RI flag was set or
because the TI flag was set--or because both flags were set. The, ISR must check the
status of these flags to determine what action is appropriate. The 8051 does not
automatically clear the RI and TI flags and it can be clear by interrupt handler.
3.Explain the memory organization of 8051 microcontroller.
The 8051 microcontroller has two types of
memory Program Memory
Data Memory
The separation of code and data memory in the 8051 is different from the usual Von
Neumann architecture, which defines that code and data can share the common
memory.
The separated memory architecture is referred to as Harvard architecture.
Program Memory:
Program memory – 64 KB of program memory includes the 4KB of the on- chip ROM. If
the address exceeds 0FFF H, it will access the external program memory. The
processor will come to know whether the user wants to use the Internal ROM or not
from the EA(active low) pin. If this pin is pulled low, it means that the user does not want
to use the Internal ROM available. The processor will 0000H-FFFFH from the external
Program Memory. If this pin is held high, the processor will access 0000H - 0FFFH from
the Internal ROM and as address goes above 0FFFH, it will access the external
Program Memory that is interfaced it
If EA (active low)= 5V
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Internal Program Memory (ROM) =0000H-0FFFH (4KB)
External Program Memory =1000H-FFFFH(60KB)
If EA (active low)= 0V
External Program Memory
=0000H-FFFFH(64KB)
Data Memory:
Data memory – 64 KB of external data memory and 128 bytes of internal data RAM and
21 special function registers. For accessing the external data memory, the processor
can either issue an 8 bit address or a 16 bit address. To access the internal data
memory, the 8 bit address is used. This 8 bit address can provide address space for
256 locations. The lower 128 addresses (0 – 127) are used as 128 bytes on chip RAM.
The upper part of the address space (128-255) is used to address the various SFR. The
Lowest 32 bytes (0-31) are reserved for 4 banks of 8 register each R0-R7,out of which
one bank may be used at any time. The working bank is specified in two bits of the
Program Status Word.
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4. Explain the port operation in 8051 microcontroller. (Nov/Dec 2015) (May/June
2015) I/O Port Configuration Each port of 8051 has bidirectional capability. Port 0 is called 'true bidirectional port' as it floats
(tristated) when configured as input. Port-1, 2, 3 are called 'quasi bidirectional port'. Port-0 Pin Structure Port-0
has 8 pins (P0.0-P0.7). The structure of a Port-0 pin is shown in fig 1
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Fig 1: Port-0 Structure
Port-1 Pin Structure:
Port-1 has 8 pins (P1.1-P1.7) .
The structure of a port-1 pin is shown in fig 2.
Fig 2 Port 1 Structure
Port-1 does not have any alternate function. It is dedicated only for I/O interfacing. When used
as output port, the pin is pulled up or down through internal pull-up. To use port-1 as input port,
'1' has to be written to the latch. In this input mode when '1' is written to the pin by the external
device then it read. When '0' is written to the pin by the external device then the external source
must sink current due to internal pull-up. If the external device is not able to sink the current the
pin voltage may rise, leading to a possible wrong reading. Port-2 has 8-pins (P2.0-P2.7) .
The structure of a port-2 pin is shown in fig 3.
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Fig 3 Port 2 Structure
Port-2 is used for higher external address byte or a normal input/output port. The I/O operation is
similar to Port-1. Port-2 latch remains stable when Port-2 pin are used for external memory
access. Due to internal pull-up there is limited current driving capability.
PORT 3 Pin Structure:
Port-3 has 8 pin (P3.0-P3.7) . Port-3 pins have alternate functions.
The structure of a port-3 pin is shown in fig 4.
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Fig 4 Port 3 Structure
Each pin of Port-3 can be individually programmed for I/O operation or for alternate function.
The alternate function can be activated only if the corresponding latch has been written to '1'.
To use the port as input port, '1' should be written to the latch. This port also has internal pull-up
and limited current driving capability.
5.Draw the pin diagram of 8051 microcontroller and explain its port structure.
Port 0(p0.0 to p0.7):
It is 8-bit bi-directional I/O port. It is bit/ byte addressable. During external memory access, it
functions as multiplexed data and low-order address bus AD0-AD7.
Port 1 (p1.0 to p1.7):
It is 8-bit bi-directional I/O port. It is bit/ byte addressable. When logic '1' is written into port latch
then it works as input mode. It functions as simply I/O port and it does not have any alternative
function. Port 0(p0.0 to p0.7):
It is 8-bit bi-directional I/O port. It is bit/ byte addressable. During external memory access, it
functions as multiplexed data and low-order address bus AD0-AD7.
Port 1 (p1.0 to p1.7):
It is 8-bit bi-directional I/O port. It is bit/ byte addressable. When logic '1' is written into port latch
then it works as input mode. It functions as simply I/O port and it does not have any alternative
function.
Port 2 (p2.0 to p2.7):
It is 8-bit bi-directional I/O port. It is bit/ byte addressable. During external memory access it
functions as higher order address bus (A8-A15).
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Port 3(p3.0 to port 3.7):
It is 8-bit I/O port. In an alternating function each pins can be used as a special function I/O pin.
P3.0-RxD:
It is an Input signal. Through this I/P signal microcontroller receives serial data of serial
communication circuit.
Fig: Pin Diagram of 8051 Microcontroller
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P3.1-TxD:
It is O/P signal of serial port. Through this signal data is transmitted.
P3.2- (INT0):
It is external hardware interrupt I/P signal. Through this user, programmer or peripheral
interrupts to microcontroller.
P3.3-(INT1):
It is external hardware interrupt I/P signal. Through this user, programmer or peripheral
interrupts to microcontroller.
P3.4- T0:
It is I/P signal to internal timer-0 circuit. External clock pulses can connects to timer-0
through this I/P signal.
P3.5-T1:
It is I/P signal to internal timer-1 circuit. External clock pulses can connects to timer-1
through this I/P signal.
P3.6-WR:
It is active low write O/P control signal. During External RAM (Data memory) access it is
generated by microcontroller. when [WR(bar)]=0, then performs write operation.
P3.7- RD:
It is active low read O/P control signal. During External RAM (Data memory) access it is
generated by microcontroller. when [RD(bar)]=0, then performs read operation from
external RAM.
XTAL1 and XTAL2:
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These are two I/P line for on-chip oscillator and clock generator circuit. A resonant
network as quartz crystal is connected between these two pin. 8051 microcontroller also
drives from external clock, then XTAL2 is used to drive 8051 from external clock and
XTAL1 should be grounded.
EA/VPP:
It is and active low I/P to 8051 microcontroller. when (EA)= 0, then 8051 microcontroller
access from external program memory (ROM) only. When (EA) = 1, then it access
internal and external program memories (ROMS).
PSEN:
It is active low O/P signal. It is used to enable external program memory (ROM). When
[PSEN(bar)]= 0, then external program memory becomes enabled and microcontroller
read content of external memory location. Therefore it is connected to (OE) of external
ROM. It is activated twice every external ROM memory cycle.
ALE:
Address latch enable: It is active high O/P signal. When it goes high, external address
latch becomes enabling and lower address of external memory (RAM or ROM) latched
into it. Thus it separates A0-A7 address from AD0-AD7. It provides properly timed signal
to latch lower byte address. The ALE is activated twice in every machine cycle. If
external RAM & ROM is not accessed, then ALE is activated at constant rate of 1/6
oscillator frequency, which can be used as a clock pulses for driving external devices.
RESET:
It is active high I/P signal. It should be maintained high for at least two machine cycle
while oscillator is running then 8051 microcontroller resets.
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UNIT- IV PERIPHERAL INTERFACING
PART - A
1. Bring about the features of 8259. (May/June-2014)
It is a programmable interrupt controller. It manages eight interrupt requests. 2.
The interrupt vector addresses are programmable. 3. The priorities of interrupts are
programmable. 4. The interrupt can be masked or unmasked individually
2. How data is transmitted in asynchronous serial communication? (May/June-
2014)
In asynchronous data transfer, one character is transferred at a time. Start and
stop bits are used with each character. The transmitter and receiver use two separate
clock inputs here.
3. What are the internal registers available in 8259 PIC? (Apr/May-2015)
Interrupt mask register (IMR), Interrupt Request register(IRR),In service
register(ISR) and Priority register(PR)
4. Distinguish between synchronous and asynchronous transmission.
(Apr/May-2015)
Asynchronous
synchronous
In this,a word or character is preceeded by a
In
this,the
transmission
begins
with a block header,
Start bit and is followed by a stop bit.
Which is a sequence of bits.
Data can be sent one character at a time
amount of data
used for transferring large
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5. What are the functions of USART? (Nov/Dec-2014)
USART stands for universal Synchronous / Asynchronous Receiver /
Transmitter. It is a programmable communication interface that can communicate by
using either synchronous or asynchronous serial data.
6. What is scan counter in 8279? (Nov/Dec-2012)
The scan counter has two modes to scan the key matrix and refresh the display.
In the encoded mode, the counter provides binary count that is to be externally decoded
to provide the scan linesfor keyboard and display. In the decoded scan mode, the
counter internally decodes the least significant 2 bit and provides a decoded 1 out of 4
scan on SL3-SL 3. The keyboard and display both are in the same mode at a time.
7. What are the basic modes of operations of 8255? (Nov/Dec-2013)
a) I/O Mode i. Mode 0- Simple Input/Output. ii. Mode 1- Strobe Input/Output
(handshake mode) iii. Mode 2- Strobe bi-directional mode b) Bit Set/Reset Mode.
8. List out the operating modes in 8253 Timer/Counter. (Nov/Dec-2014)
Mode 0 : Interrupt on terminal count
MODE 1 : Hardware Retriggerable One-shot
MODE 2 : Rate generator
MODE 3 : Square Wave Rate Generator
MODE 4 : Software Triggered Strobe.
MODE 5 : Hardware triggered strobe (Retriggerable).
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9. Give the control word format of 8253 Timer. (May/June-2012)
10. What is BSR mode in 8255? (Nov/Dec-2012)
11. What are the different peripheral interfacing used with 8085 microprocessor?
(May/June-2013)
Keyboard, Memory, EPROM, LCD display, LED seven segment displays.
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12. What are the output terminals in USART 8251? (May/June-2013)
TXD (output terminal), TXRDY (output terminal), TXEMPTY (Output terminal), RXRDY
(Output terminal), DTR (Output terminal), RTS (Output terminal)
13. What are the different types of command words used in 8259A? (Nov/Dec-
2013) The command words of 8259A are classified in two groups 1. Initialization command words (ICWs) 2. Operation command words (OCWs)
14. What are the basic modes of operation of 8255? (Nov/Dec-2013)
Mode 0: Basic Input/output
Mode 1: Strobes Input/output
Mode 2: Bi-direction bus.
15. How data is transmitted in asynchronous serial communication?
(May/June-2014)
In this the data is transferred bit by bit that is used for one to one communication.
PART - B
1.Draw the block diagram of 8255A Programmable Peripheral Interface (PPI) and
explain each block . (May/June-2014)
The Programmable Peripheral Interface (PPI) chip is a peripheral chip.It is made in 40
pin DIP. The 8255 is used to give the CPU access to programmable parallel I/O.. The
8255 has 24 input/output pins in all.These are divided into three 8-bit ports.
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Port A and port B can be used as 8-bit input/output ports.Port C can be used as an 8-
bit input/output port or as two 4-bit input/output ports or to produce handshake signals
for ports A and B.
The three ports are further grouped as follows:
1. Group A consisting of port A and upper part of port C.
2. Group B consisting of port B and lower part of port C. Eight data lines (D0 - D7) are available to read/write data into the ports or control
register.The RD andWR pin , which are active low signals for read and write operations.
The address lines A1 and A0 allow to successively access any one of the ports or the
control register.The control signal chip select CS is used to enable the 8255 chip. when
CS = '0', the 8255 is enabled.The RESET input is connected to the RESET
pin8085.When the system is reset, all the ports are initialized as input lines.
The control register or the command word register is an 8-bit register used to select the
modes of operation and input/output designation of the ports.
Operational modes of 8255
There are two basic operational modes of 8255:
Bit set/reset Mode (BSR Mode).
Input/Output Mode (I/O Mode).
Bit set/reset (BSR) mode
The Bit Set/Reset (BSR) mode is applicable to port C only.Each line of port C (PC0 -
PC7) can be set/reset by suitably loading the control word register. BSR mode and I/O
mode are independent and selection of BSR mode does not affect the operation of
other ports in I/O mode.
A1 A0 Port Selected
0 0 Port A
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0 1 Port B
1 0 Port C
1 1 Control Word Register
BLOCK DIAGRAM OF INTEL 8255:
CONTROL WORD FOR BSR MODE:
D7 D6 D5 D4 D3 D2 D1 D0
0 * * * B2 B1 B0 S/R
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D7 bit is always 0 for BSR mode.
Bits D6, D5 and D4 are don't care bits.
Bits D3, D2 and D1 are used to select the pin of Port C.
Bit D0 is used to set/reset the selected pin of Port C.
Selection of port C pin is determined as follows:
B2 B1 B0 Pin of Port C Selected
0 0 0 PC0
0 0 1 PC1
0 1 0 PC2
0 1 1 PC3
1 0 0 PC4
1 0 1 PC5
1 1 0 PC6
1 1 1 PC7
INPUT/OUTPUT MODE
This mode is selected when D7 bit of the Control Word Register is 1. There are three
I/O modes
1. Mode 0 - Simple I/O
2. Mode 1 - Strobed I/O
3. Mode 2 - Strobed Bi-directional I/O
CONTROL WORD FORMAT FOR I/O MODE:
D7 D6 D5 D4 D3 D2 D1 D0
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Mode 0 - Simple I/O
In this mode, the ports can be used for simple I/O operations without handshaking
signals.
Port A- 8 bit port.
Port B – 8 bit port.
Port C – two 4 bit ports.(Port C upper & Port C lower)
Mode 0 features:
Output ports are latched.Input ports are buffered, not latched.Ports do not have
handshake or interrupt capability.With 4 ports, 16 different combinations of I/O are
possible. Mode 1:- Strobed I/O
Port A or Port B for handshake (strobed) input or output operation.
Port A + Port C upper function as handshake signals.
Port B + Port C lower function as handshake signals.
Mode 1 features:
Two ports i.e. port A and B can be used as 8-bit i/o ports.Each port uses three lines of
port c as handshake signal and remaining two signals can be used as i/o ports.Interrupt
logic is supported.Input and Output data are latched.
Input Handshaking signals
1. IBF (Input Buffer Full)
2. STB (Strobed Input)
3. INTR (Interrupt request)
4. INTE (Interrupt enable)
Output Handshaking signals
1. OBF (Output Buffer Full)
2. ACK (Acknowledge)
3. INTR (Interrupt request)
4. INTE (Interrupt enable)
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Mode 2:Strobed Bidirectional I/O
Port A can be used for bidirectional handshake data transfer. Pins PC4 - PC7 are used
as handshake lines for port A.Acknowledgement and handshaking signals are provided
to maintain proper data flow and synchronization between the data transmitter and
receiver.
2.Discuss the internal architecture of 8253/8254 Programmable Interval timer.
(May/June-2014)
The Intel 8253 and 8254 are Programmable Interval Timers (PITs), which perform
timing and counting functions and has the same pinout.
8253 8254
Operating frequency is 0-2.6 Mhz. Operating frequency is 0-10 Mhz.
Uses N-MOS technology. Uses H-MOS technology.
Read Back command is not available. Read Back command is available.
Reads and Writes of the same counter Reads and Writes of the same counter can
cannot be interleaved. be interleaved.
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BLOCK DIAGRAM OF INTEL 8253/8254
The timer has three counters.or timers which are named as "Counter 0", "Counter 1"
and "Counter 2".Each counter has 2 input pins – "CLK" (clock input) and "GATE" – and
1-pin, "OUT", for data output. The 3 counters are 16-bit down counters independent of
each other, and can be easily read by the CPU. The first counter is used to generate
atimekeeping interrupt.The second counter is used to trigger the refresh of DRAM
memory. The last counter is used to generate tones via the PC speaker. Data/Bus Buffer: This block contains the logic to buffer the data bus to / from the microprocessor, and to
the internal registers. It has 8 input pins, usually labelled as D7..D0, where D7 is the
MSB.
Read/Write Logic: The Read/Write Logic block has 5 pins.
/RD: read signal
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/WR: write signal
/CS: chip select signal
A0, A1: address lines
Control Word Register:
To initialize the counters, the microprocessor must write a control word (CW) in this
register. This can be done by setting proper values for the pins of the Read/Write Logic
block and then by sending the control word to the Data/Bus Buffer block.The control
word register contains 8 bits, labeled D7..D0 (D7 is the MSB).
D7 D6 D5 D4 D3 D2 D1 D0
SC1 SC2 RW1 RW0 M2 M1 M0 BCD
D0 – 1 = BCD Counter , 0 – Binary Counter
D3 D2 D1
M2 M1 M0 Mode
0 0 0 Mode0
0 0 1 Mode1
X 1 0 Mode2
X 1 1 Mode3
1 0 0 Mode4
1 0 1 Mode5
D5 D4
RW1 RW0 Operation
0 0 Counter Latching Operation
0 1 Read/Write LSB only
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1 0 Read/Write MSB only
1 1 Read/Write LSB and then MSB
D7 D6
SC1 SC0 Operation
0 0 Select Counter 0
0 1Select Counter 1 1 0Select Counter 2
1 1Illegal
READ BACK COMMAND (ONLY AVAILABLE IN 8254)
D7 D6 D5 D4 D3 D2 D1 D0
1 1 COUNT STATUS CNT2 CNT1 CNT0 0
D5 – 0 = Latch Count of Selected Counters.
D4 – 0 = Latch Status of Selected Counters.
D3 – 1 = Select Counter 2
D2 – 1 = Select Counter 1
D1 – 1 = Select Counter 0
Operation Modes
Mode 0 : Interrupt on Terminal Count
Mode 0 is used for the generation of accurate time delay under software control. In this
mode, the counter will start counting from the initial COUNT value loaded into it, down
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to 0.Counting rate is equal to the input clock frequency.The OUT pin is set low after the
Control Word is written, and counting starts one clock cycle after the COUNT
programmed. OUT remains low until the counter reaches 0, at which point OUT will be
set high until the counter is reloaded or the Control Word is written. The Gate signal
should remain active high for normal counting. If Gate goes low counting gets
terminated and current count is latched till Gate pulse goes high again.
Mode 1 : Programmable One Shot
In this mode 8253 can be used as MonostableMultivibrator.GATE input is used as
trigger input.OUT will be initially high. OUT will go low on the CLK pulse following a
trigger to begin the one-shot pulse, and will remain low until the Counter reaches zero.
OUT will then go high and remain high until the CLK pulse after the next trigger.
Mode 2: Rate Generator
In this mode, the device acts as a divide-by-n counter, which is commonly used to
generate a real-time clock interrupt.Counting process will start the next clock cycle after
COUNT is sent. OUT will then remain high until the counter reaches 1, and will go low
for one clock pulse.OUT will then go high again, and the whole process repeats itself.
Mode 3 : Square Wave Generator
This mode is similar to mode 2. The duration of the high and low clock pulses of the
output will be different from mode 2.If „N „is the number loaded into the counter , the
output will be
High for N/2 counts and N/2 counts for Low if N is Even.
High for (N+1)/2 counts and (N-1)/2 counts for Low if N is Odd.
Mode 4 : Software Triggered Strobe
After Control Word and COUNT is loaded, the output will remain high until the counter
reaches zero.The counter will then generate a low pulse for 1 clock cycle (a strobe) –
after that the output will become high again.
Mode 5 : Hardware Triggered Strobe
This mode is similar to mode 4. However, the counting process is triggered by the
GATE input.After receiving the Control Word and COUNT, the output will be set high.
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When the GATE input is high , it will start counting. When the counter reaches 0, the
output will go low for one clock cycle – after that it will become high again, to repeat the
cycle.
3.Draw and explain the functional block diagram of 8259 Programmable Interrupt
Controller. (Apr/May-2015)
Functional Description:
The 8259 A has eight interrupt request inputs, IR0- IR7.The 8259 A uses its INT output
to interrupt the 8085A via INTR pin.The 8259Areceives interrupt acknowledge pulses
from the at its input.Vector address used by the 8085 A to transfer control to the service
subroutine of the interrupting device, is provided by the 8259 A on the data bus.
The 8259A is a programmable device that must be initialized by command words sent
by the. After initialization the 8259A mode of operation can be changed by operation
command words. The descriptions of various blocks are,
Data bus buffer:
This 3- state, bidirectional 8-bit buffer is used to interface the 8259Ato the system data
bus. Control words and status information are transferred through the data bus buffer.
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Read/Write & control logic:
The function of this block is to accept OUTPUT commands from the CPU. It contains
the initialization command word (ICW) register and operation command word OCW)
register which store the various control formats for device operation. This function block
also allows the status of 8259A to be transferred to the data bus. Interrupt request register (IRR):
IRR stores all the interrupt inputs that are requesting service.It keeps track of which
interrupt inputs are asking for service. If an interrupt input is unmasked, and has an
interrupt signal on it, then the corresponding bit in the IRR will be set. Interrupt mask register (IMR):
The IMR is used to disable (Mask) or enable (Unmask) individual interrupt inputs.Each
bit in this register corresponds to the interrupt input with the same number.The IMR
operation on the IRR. Maskingof higher priority input will not affect the interrupt request
lines oflower priority.To unmask any interrupt the corresponding bit is set „0‟.
In service register (ISR):
The in service registers keeps tracks of which interrupt inputs are currently being
serviced.For each input that is currently being serviced the corresponding bit will be set
in the in service register.Each of these 3-reg can be read as status reg.Priority
Resolver:
This logic block determines the priorities of the set in the IRR. The highest priority is
selected and strobed into the corresponding bit of the ISR during pulse. Cascade buffer/comparator:
This function blocks stores and compare the address of all 8259A‟s in the register.The
associated 3-I/O pins (CAS0-CAS2) are outputs when8259A is used a master.As a
master, the 8259A sends the ID of the interrupting slave device onto the cas2-cas0.The
slave thus selected will send its pre-programmed subroutine address on to the data bus. Priority Modes of 8259 :
The priority modes availaible in 8259 is
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Fully Nested Mode
Automatic Rotation Mode
Specific Rotation Mode
Fully Nested Mode:
This is a general purpose mode in which all IR‟s are arranged from highest to
lowest ie.IR0 is the highest and IR7 is the lowest one.Any IR can be assigned the
highest priority,the priority sequence will begin at that IR. Automatic Rotation Mode:
In this mode, a device which one is being serviced will be considered as a lowest
priority In the next time.
Specific Rotation Mode:
This mode is similar to the automatic rotation mode except the user can select
any IR for the lowest priority, thus fixing any other priorities.
End of Interrupts (EOI):
After the completion of an interrupt service, the corresponding ISR bit needs to
be reset.This is called the End of Interrupt.(EOI).It can be issued in 3 formats.They are
Non Specific EOI Command:
When the 8259 receives this command,it resets the highest priority ISR bit.
Specific EOI Command:
It specifies which ISR bit to be reset.
Automatic EOI Command:
When the 8259 receives the third INTA signal, the ISR bit is reset.The major
drawback of this mode is that ISR does not have information on which IR is being
serviced.
There are four Initialization Command Word ICW1,ICW2,ICW3&ICW4 and
three Operation Control Word OCW1,OCW2 &OCW3
Initialization Command Word 1 (ICW1)
D7 D6 D5 D4 D3 D2 D1 D0
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A7 A6 A5 1 LTIM ADI SNGL IC4
D0- 1=ICW4 is needed, 0= No ICW4 needed D1-
1=Single 8259, 0=Cascading 8259's D2- 1=Interval
of 4,0=Interval of 8 D3- 1=level triggered mode,
0=edge triggered mode D5,D6,D7 – Interrupt
Vector Address
Initialization Command Word 2 (ICW2)
D7 D6 D5 D4 D3 D2 D1 D0
A15/T7 A14/T6 A13/T5 A12/T4 A11/T3 A10 A9 A8
A15-A7 – Interrupt Vector Address (8085 mode)
T7 – T3 - Interrupt Vector Address (8086 mode)
Operation Control Word 1 ( OCW1)
D7 D6 D5 D4 D3 D2 D1 D0
M7 M6 M5 M4 M3 M2 M1 M0
M7-M0 – 1 – Interrupt Mask Set
0 – Interrupt Mask Reset
4.Draw the neat diagram ,explain the architecture and features of 8279 keyboard /
display controller. (Apr/May-2015)
Block Diagram of Keyboard/Display Controller
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The Keyboard/Display Controller 8279Intel‟s 8279 is a general purpose Keyboard
Display controller that simultaneously drives the display of a system and interfaces a
Keyboard with the CPU. The Keyboard Display interface scans the Keyboard to identify
if any key has been pressed and sends the code of the pressed key to the CPU.It also
transmits the data received from the CPU,to the display device.The Keyboard display
controllerchip8279provides1. A set of four scan lines and eight return lines for
interfacingkeyboards.2. A set of eight output lines for interfacing display.
I/OControlandDataBuffer
The I/O control section controls the flow of data to/from the 8279. The data buffer
interface the external bus of the system with internal bus of 8279. The pin Ao, RD and
WR select the command, status or data read/write operations carried out by the CPU
with 8279.
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Control and Timing Register and Timing Control
These registers store the keyboard and display modes and other operating conditions
programmed by CPU.The registers are written with Ao=1 and WR =0.The timing and
control unit controls the basic timings for the operation of the circuit.Scan Counter divide
down the operating frequency of 8279 to derive scan keyboard and scan display
frequencies.
Scan Counter
The Scan Counter has two modes to scan the key matrix and refresh the display.In the
Encoded mode, the counter provides a binary count that is to be externally decoded to
provide the scan lines for keyboard and display.In the decoded scan mode, the counter
internally decodes the least significant 2 bits and provides a decoded 1 out of 4 scan on
SL0-SL3.The Keyboard and Display both are in the same mode at a time.
Return Buffers and Keyboard Debounce and Control
This section scans for a Key closure row-wise.If it is detected, the Keyboard debounce
unit debounces the key entry.After the debounce period, if the key continues to be
detected. The code of the Key is directly transferred to the sensor RAM along with
SHIFT and CONTROL key status.
FIFO/Sensor RAM and Status Logic
In Keyboard or strobed input mode, this block acts as 8-byte first-in-first-out (FIFO)
RAM. Each key code of the pressed key is entered in the order of the entry, and in the
meantime, read by the CPU, till the RAM becomes empty. The status logic generates
an interrupt request after each FIFO read operation till the FIFO is empty.In scanned
sensor matrix mode, this unit acts as sensor RAM.Each row of the sensor RAM is
loaded with the status of the corresponding row of sensors in the matrix.If a sensor
changes its state, the IRQ line goes high to interrupt the CPU.
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Display Address Registers and Display RAM.
The Display address registers hold the addresses of the word currently being written or
read by the CPU to or from the display RAM.The contents of the registers are
automatically updated by 8279 to accept the next data entry by CPU. The 16-byte
display RAM contains the 16-byte of data to be displayed on the sixteen 7-seg displays
in the encoded scan mode. DetailsofModesofOperation
Keyboard Modes
Scanned Keyboard Mode with 2 Key Lockout
In this mode of operation, when a key is pressed, a debounce logic comes into
operation. The Key code of the identified key is entered into the FIFO with SHIFT and
CNTL status, provided the FIFO is not full. Scanned Keyboard with N-key Rollover
In this mode, each key depression is treated independently. When a key is pressed, the
debounce circuit waits for 2 keyboard scans and then checks whether the key is still
depressed. If it is still depressed, the code is entered in FIFO RAM. Any number of keys
can be pressed simultaneously and recognized in the order, the Keyboard scan record
them. ScannedKeyboardSpecialErrorMode
This mode is valid only under the N-Key rollover mode. This mode is programmed using
end interrupt/error mode set command. If during a single debounce period (two
Keyboard scan) two keys are found pressed, this is considered a simultaneous
depression and an error flag is set. This flag, if set, prevents further writing in FIFO
butallows generation of further interrupts to the CPU for FIFO read.
SensorMatrixMode
In the Sensor Matrix mode, the debounce logic is inhibited the 8-byte memory matrix.
The status of the sensor switch matrix is fed directly to sensor RAM matrix Thus the
sensor RAM bits contains the row-wise and column-wise status of the sensors in the
sensor matrix.
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DisplayModes
There are various options of data display The first one is known as left entry mode or
type writer mode. Since in a type writer the first character typed appears at the left-most
position, while the subsequent characters appears successively to the right of the first
one.The other display format is known as right entry mode, or calculator mode, since
the calculator the first character entered appears at the right-most position and this
character is shifted one position left when the next character is entered.
1.LeftEntryMode
In the Left entry mode, the data is entered from the left side of the display unit.
Address0 of the display RAM contains the leftmost display character and address 15
of the RAM contains the rightmost display character.
2.RightEntryMode
In the right entry mode, the first entry to be displayed is entered on the rightmost
display.The next entry is also placed in the right most display but after the previous
display is shifted left by one display position.
All the Command words or status words are written or read with Ao = 1 and CS = 0 to or
from 8279.
a. Keyboard/ Display mode set
The format of the command word to select different modes of operation of 8279 is given
below with its bit definitions.
D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 D D K K K
D4 D3 Display Modes
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0 0 8*8 Character Left Entry
0 1 16*8 Character Left Entry
1 0 8*8 Character Right Entry
1 1 16*8 Character Left Entry
D2 D1 D0 Keyboard Modes
0 0 0 Encoded Scan 2 Key lock
out
0 0 1 Decoded Scan 2 Key lock
out
0 1 0 Encoded Scan N Key
rollover
0 1 1 Decoded Scan N Key
rollover
1 0 0 Encoded Scan Sensor
Matrix
1 0 1 Decoded Scan Sensor
Matrix
1 1 0 Strobed Input Encoded
Scan
1 1 1 Strobed Input Decoded
Scan
5.Draw the neat diagram ,explain the architecture and features of 8237Direct
Memory Access
Controller.
DMA Controller: A DMA controller is a device, usually peripheral to a CPU that is
programmed to perform a sequence of data transfers on behalf of the CPU.A DMA
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controller can directly access memory and is used to transfer data from one memory
location to another, or from an I/O device to memory and vice versa.A DMA controller
manages several DMA channels, each of which can be programmed to perform a
sequence of these DMA transfers.A DMA request signal for each channel is routed to
the DMA controller.When the DMA controller sees a DMA request, it responds by
performing one or many data transfers from that I/O device into system memory or vice
versa.Channels must be enabled by the processor for the DMA controller to respond to
DMA requests.A DMA controller typically shares the system memory and I/O bus with
the CPU and has both bus master and slave capability. The diagram of DMA controller
architecture and how the DMA controller interacts with the CPU.In bus master mode,
the DMA controller acquires the system bus (address, data, and control lines)from the
CPU to perform the DMA transfers. Because the CPU releases the system bus for the
duration of the transfer, the process is sometimes referred to as cycle stealing.In bus
slave mode, the DMA controller is accessed by the CPU, which programs the
DMAcontroller's internal registers to set up DMA transfers.The internal registers consist
of source and destination address registers and transfer count registers for each DMA
channel, as well as control and status registers for initiating, monitoring, and sustaining
the operation of the DMAcontroller.
DMA Transfer Types and Modes :
DMA controllers vary as to the type of DMA transfers and the number of DMA
channels. The two types of DMA transfers are
i) flyby DMA transfers
ii) fetch-and-deposit DMAtransfers.
iii) The three common transfer modes are single, block, and
demand transfer modes.
A 8237 DMA controller IC :
CLK: CLOCK INPUT:
The Clock Input is used to generate the timing signals which control82C37A
operations.
105
CS: CHIP SELECT:
Chip Select is an active low input used to enable the controller onto thedata bus for
CPU communications.
Fig:Architecture of DMA Controller RESET:
This is an active high input which clears the Command, Status, Request, and
Temporary registers, the First/Last Flip-Flop, and the mode register counter.The Mask
registeris set to ignore requests.
READY:
This signal can be used to extend the memory read and write pulses from the
82C37A to accommodate slow memories or I/O devices.
HLDA: HOLD ACKNOWLEDGE:
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The active high Hold Acknowledge from the CPU indicates that it has
relinquished control of the system busses.
DREQ0-DREQ3: DMA REQUEST:
The DMA Request (DREQ) lines are individual asynchronous channel request
inputs used by peripheral circuits to obtain DMA service.In Fixed Priority, DREQ0 has
the highest priority and DREQ3 has the lowest priority.A request is generated by
activating the DREQ line of a channel. DACK will acknowledge the recognition of a
DREQ signal.RESET initializes these lines to active high.DREQ must be maintained
until the corresponding DACK goes active.DREQ will not be recognized while the clock
is stopped.Unused DREQ inputs should be pulled High or Low(inactive) and the
corresponding mask bit set.
DB0-DB7: DATA BUS:
The Data Bus lines are bidirectional three-state signals connected to the system
data bus. The outputs are enabled in the Program condition during the I/O Read to
output the contents of a register to the CPU.The outputs are disabled and the inputs are
read during an I/O Write cycle when the CPU is programming the 82C37A control
registers. During DMA cycles, the most significant 8-bits of the address are output onto
the data bus to be strobed into an external latch by ADSTB. In memory-to-memory
operations, data from the memory enters the 82C37A on the data bus during the read-
from-memory transfer, then during the write-to memory transfer, the data bus outputs
write the data into the new memory location.
IOR: READ:
I/O Read is a bidirectional active low three-state line. In the Idle cycle, it is an
input control signal used by the CPU to read the control registers. In the active cycle, it
is an output control signal used by the 82C37A to access data from the peripheral
during a DMAWrite transfer.
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IOW: WRITE:
I/O Write is a bidirectional active low three-state line.
In the Idle cycle, it is an input control signal used by the CPU to load information into
the 82C37A. In the active cycle, it is an output control signal used by the 82C37A to
load data to the peripheral during a DMA
Read transfer.
EOP: END OF PROCESS:
End of Process (EOP) is an active low bidirectional signal.The 82C37A allows an
external signal to terminate an active DMA service by pulling the EOP pin low.A pulse is
generated by the 82C37A when terminal count (TC) for any channel is reached, except
for channel 0 in memory-to-memory mode.During memory-to-memory transfers , EOP
will be output when the TC for channel 1 occurs.The EOP pin is driven by an open drain
transistor on-chip, and requires an external pull-up resistor to VCC. When an EOP pulse
occurs, whether internally or externally generated, the 82C37A will terminate the
service,and if auto-initialize is enabled, the base registers will be written to the current
registers of that channel. The mask bit and TC bit in the status word will be set for the
currently active channel by EOP unless the channel is programmed for auto initialize. In
that case, the mask bit remains clear.
A0-A3: ADDRESS: The four least significant address lines are bidirectional three-state
signals. In the Idle cycle, they are inputs and are used by the 82C37A to address the
control register to be loaded or read. In the Active cycle, they are outputs and provide
the lower 4-bits of the output
address.
A4-A7: ADDRESS: The four most significant address lines are three-state outputs and
provide 4-bits of address. These lines are enabled only during the DMA service.
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HRQ: HOLD REQUEST: The Hold Request (HRQ) output is used to request control of
the system bus. When a DREQ occurs and the corresponding mask bit is clear, or a
software DMA request is made, the 82C37A issues HRQ. The HLDA signal then
informs the controller when access to the system busses is permitted. For stand-alone
operation where the 82C37A always controls the busses, HRQ may be tied to HLDA.
This will result in one S0 state before the transfer.
DACK0-DACK3: DMA ACKNOWLEDGE:
DMA acknowledge is used to notify the individual peripherals when one has been
granted a DMA cycle. RESET initializes them to active low.
AEN: ADDRESS ENABLE:
Address Enable enables the 8-bit latch containing the upper 8address bits onto the
system address bus. AEN can also be used to disable other system busdrivers during
DMA transfers.AEN is active high.
ADSTB: ADDRESS STROBE:
This is an active high signal used to control latching of the upper address byte. During
block operations, ADSTB will only be issued when the upper address byte must be
updated. ADSTB timing is referenced to the falling edge of the 82C37A clock.
MEMR: MEMORY READ:
The Memory Read signal is an active low three-state output used to access data from
the selected memory location during a DMA Read or a memory-to-memory transfer.
MEMW MEMORY WRITE:
The Memory Write signal is an active low three-state output used to write data to the
selected memory location during a DMA Write or a memory-to-memory transfer.
NC: NO CONNECT: Pin 5 is open and should not be tested for continuity.
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Functional Description
The 82C37A direct memory access controller is designed to improve the data
transfer rate in systems which must transfer data from an I/O device to memory, or
move a block of memory to an I/O device. It will also perform memory-to-memory block
moves, or fill a block of memory with data from a single location. Operating modes are
provided to handle single byte transfers as well as discontinuous data streams, which
allows the 82C37A to control data movement.Memory-to-memory operations require
temporary internal storage of the data byte between generation of the source and
destination addresses, so memory-to-memory transferstake place at less than half the
rate of I/O operations, but still much faster than with centralprocessor techniques. The
block diagram of the 82C37A consists of timing and control block, priority block, and
internal registers are the main components. The timing and control block derives
internal timing from clock input, and generates external control signals. The Priority
Encoder block resolves priority contention between DMA channels requesting service
simultaneously.
DMA Operation:
In a system, the 82C37A address and control outputs and data bus pins are basically
connected in parallel with the system busses. An external latch is required for the upper
address byte. While inactive, the controller‟s outputs are in a high impedance state.
When activated by a DMArequest and bus control is relinquished by the host, the
82C37A drives the busses and generates the control signals to perform the data
transfer.The operation performed by activating one of the four DMA request inputs has
previously been programmed into the controller via the Command,Mode, Address, and
Word Count registers.For example, if a block of data is to be transferredfrom RAM to an
I/O device, the starting address of the data is loaded into the 82C37A Current and Base
Address registers for a particular channel, and the length of the block is loaded into the
channel‟s Word Count register. The corresponding Mode register is programmed for a
memory to-I/O operation (read transfer), and various options are selected by the
Command register and the other Mode register bits.The channel‟s mask bit is cleared to
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enable recognition of a DMArequest (DREQ). The DREQ can either be a hardware
signal or a software command. Once initiated, the block DMA transfer will proceed as
the controller outputs the data address,simultaneous MEMR and IOW pulses, and
selects an I/O device via the DMA acknowledge(DACK) outputs.The data byte flows
directly from the RAM to the I/O device. After each byte is transferred, the address is
automatically incremented (or decremented) and the word count is decremented.The
operation is then repeated for the next byte. The controller stops transferring data when
the Word Count register underflows, or an external EOP is applied.
UNIT V
MICRO CONTROLLER PROGRAMMING & PPLICATIONS
PART -A
1. What are the applications of 8051 Microcontroller? (M/J ‘12’)
(i) Washing Machine control, (ii) Traffic Light control, (iii) Servo Motor control, (iv)
Stepper motor control, (v) DC motor control.
2.What are the 3 classes of data transfer instructions?
General purpose transfer
Accumulator specific transfer
Address object transfer
3.What are the 3 classes of control transfer instruction?
Unconditional calls, returns and jumps
Conditional jumps
Interrupts
4.Write about CALL statement in 8051?(Nov/Dec 2012)
There are two subroutine CALL instructions. They are
*LCALL(Long CALL)
*ACALL(Absolute CALL)
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Each increments the pc to the 1st byte of the instruction & pushes them in to the stack.
5.Write about the jump statement?
There are three forms of jump. They are
LJMP(Long-jump)-address 16
AJMP(Absolute jump)-address 11
SJMP(short jump)-relative address
6.Write a program to find 2’s complement using 8051?
MOV A,R0
CPL A
INC A
7.Write a program to swap two numbers using 8051?
MOV A,#data
SWAP A
8. Mention the interrupts of 8051 microcontroller? (Nov/Dec ‘13’) INT0, TF0, INT1, TF1, R1 & T1
9.What is a stepper motor?(Nov/Dec 2014)
A stepper motor is a specially constructed DC motor with 4 windings. It rotates in
precise steps with a common step size range of 0.9 to 30 degrees.
10.Write the coil sequence for a full step rotation of a stepper motor.(May/June
2013)
Clockwise B2 B1 A2 A1 Anti
clockwise D3 D2 D1 D0
1 1 0 0
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1 0 0 1
0 0 1 1
0 1 1 0
1 1 0 0
11.What are the tasks involved in keyboard interfacing?
The task involved in keyboard interfacing are
Sensing a keyboard
Sensing a key actuation
De bouncing the key and
Generating key codes .
12. How a keyboard matrix is formed in keyboard interface ?
The return lines RL0 to RL7 of 8279 are used to form the columns of keyboard matrix
and decoded scan the scan lines SLO to SL3 of 8279 are used to form the rows of
keyboard matrix.
Inencoded scan mode, the output lines of external decoder are used as rows of
keyboard matrix.
13. What is scanning in keyboard and what is scan time?
The process of sending a zero to each row of a keyboard matrix and reading the
columnsfor key actuation is called scanning. The scan time is the time taken by the
processor to scan allthe rows one by one starting from first row and coming back to the
first row.
14.Why a driver circuit is used while connecting a microprocessor to relay?
Microcontroller pin lacks sufficient current to drive the relay. So a driver circuit or power
transistor is placed between the microcontroller and the relay.
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15.How the speed of an electric motor is controlled?
The speed of an electric motor is controlled by controlling the power source of the
motor. To provide a variable power supply, a variable series resistance is placed
between the motor and supply.
PART -B
1.Explain the different types of instruction of 8051. (May/June 2012)
8051 has about 111 instructions. These can be grouped into the following categories.
1.Data Transfer instructions
2. Arithmetic Instructions
3. Logical Instructions
4. Program Branching (Control transfer) Instructions
1.Data Transfer Instructions
The data transfer instruction is used to (copy) transfers data from source location
to destination location.
Syntax:
MOV Rn , Rn
Ex:MOV A,R0
This instruction transfers data from R0 register to Accumulator.
Syntax:
MOV A, direct
Ex:MOV A,40H
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This instruction transfers data from 40H location to Accumulator.
Syntax:
MOV A, @Ri
Ex: MOV A, @R0
This instruction transfers data from the content of R0 as a location to
Accumulator.
Syntax:
MOV A, #data
EX: MOV A, # 40H
This instruction transfers immediate data 40H to Accumulator.
2.Arithmetic Instructions:
Thearithmeticinstructionsincludesaddition,subtraction,multiplication,division,increment,d
ecrement and etc.
Syntax:
ADD Rn , Rn
Ex:ADD A,R0
This instruction adds data from R0 register and Accumulator and finally result is
stored in Acc.
Syntax:
ADD A, direct
Ex:ADD A,40H
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This instruction adds data from 40H location and Accumulator and finally result is
stored in Acc.
Syntax:
ADD A, @Ri
Ex: ADD A, @R0
This instruction adds data from the content of R0 as a location and Accumulator
and finally result is stored in Acc..
Syntax:
ADD A, #data
EX: ADD A, # 40H
This instruction adds immediate data 40H and Accumulator and finally result is
stored in Acc..
3.Logical Instructions
The logical instructions includes AND,OR,EXOR,Rotate instructions.
Syntax:
ANLRn , Rn
Ex:ANL A,R0
This instruction AND with data from R0register,Accumulator and finally result is
stored in Acc.
Syntax:
ANL A, direct
Ex:ANL A,40H
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This instruction AND with data from 40H location,Accumulator and finally result is
stored in Acc.
Syntax:
ANL A, @Ri
Ex: ANL A, @R0
This instruction AND with data from the content of R0 as a location,Accumulator
and finally result is stored in Acc..
Syntax:
ANL A, #data
EX: ANL A, # 40H
This instruction AND immediate data 40H ,Accumulator and finally result is
stored in Acc..
5.Control Transfer Instructions
ACALL addr11
Absolute Call to relative address
AJMP addr11
Asolute Jump to relative address
CJNE A, direct, rel
Compare with A with memory location content if not equal then jump to relative address.
DJNZ Rn, rel
Decrement Rn, and jump if not zero to relative address
JC rel
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Jump if carry to relative address
JNC rel
Jump if no carry to relative address
2.Explain in detail about 8051 Addressing Modes(May/June 2014)
8051 has four addressing modes.
1.Register Addressing.
2.Direct Addressing.
3.Register Indirect Addressing.
4.Immediate Addressing
5.Base plus Index Register Addressing.
1.Register Addressing:
This way of addressing accesses the bytes in the current register bank.
Data is available in the register specified in the instruction.
The register bank is decided by 2 bits of ProgramStatusWord (PSW).
Example-
ADD A, R0
This instruction Adds content of R0 to A and stores in A
2.Direct Addressing:
The address of the data is available in the instruction.
Example -
MOV A, 88H;
Moves the content of address 88Hto A.
3.Register Indirect Addressing:
The address of data is available in the R0 or R1 registers as specified in the
instruction.
Example –
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MOV A, @R0
Moves content of address pointed by R0 to A .
4.Immediate Addressing:
Data is immediately available in the instruction.
Example -
ADD A, #77H
Adds 77 H to A and stores in A
5.Base plus Index Register Addressing.
The content of base register and index register content is added to locate the
data.
Example -
MOVC A, @A+DPTR
Moves content of address pointed by A+DPTR to A
3. Draw the schematic for interfacing a stepper motor with 8051 microcontroller
and write 8051 ALP for changing speed and direction of motor. The complete board consists of transformer, control circuit, keypad and stepper motor .
The circuit has inbuilt 5 V power supply so when it is connected with transformer it will
give the supply to circuit and motor both.
The 8 Key keypad is connected with circuit through which user can give the command
to control stepper motor. The control circuit includes micro controller 89C51, indicating
LEDs, and current driver chip ULN2003A. By giving different commands the stepper
motor can run clockwise, run anticlockwise, increase/decrease RPM,increase/decrease
revolutions, stop motor, change the mode, etc. Stepper motor has four coils.One end of
each coil is tied together and it gives common terminal which is always connected with
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positive terminal of supply. The other ends of each coil are given for interface. Specific
color code may also be given.
First Coil L1-Orange
Second Coil L2 -Brown
Third Coil L3 - Yellow
Fourth Coil L4 - Black
Common Terminal -Red
By means of controlling a stepper motor operation we can
1. Increase or decrease the RPM (speed) of it 2. Increase or decrease number of revolutions of it 3. Change its direction means rotate it clockwise or anticlockwise
Fig:Interfacing of stepper motor with 8051 Microcontroller
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To vary the RPM of motor we have to vary the PRF (Pulse Repetition Frequency).
Number of applied pulses will vary number of rotations and last to change direction we
have to change pulse sequence. So all these three things just depends on applied
pulses. Now there are three different modes to rotate this motor 1. Single coil excitation 2. Double coil excitation 3. Half step excitation
Pulses for stepper motor module
Clockwise B2 B1 A2 A1 Anti
clockwise D3 D2 D1 D0
1 1 0 0
1 0 0 1
0 0 1 1
0 1 1 0
1 1 0 0
The circuit consists of very few components. The major components are 7805, 89C51
and ULN2003A.
Connections:-
1. The transformer terminals are given to bridge rectifier to generate rectified DC. 2. It is filtered and given to regulator IC 7805 to generate 5 V pure DC. LED
indicates supply is ON. 3. All the push button micro switches J1 to J8 are connected with port P1 as shown to
form serial keyboard. 4. 12 MHz crystal is connected to oscillator terminals of 89C51 with two biasing
capacitors. 5. All the LEDs are connected to port P0 as shown 6. Port P2 drives stepper motor through current driver chip ULN2003A. 7. The common terminal of motor is connected to Vcc and rest all four terminals are
connected to port P2 pins in sequence through ULN chip.
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4. Draw the schematic for interfacing a servo motor with 8051 microcontroller and
write for servo motor control. (Nov/Dec 2014)
Servo motors are self-contained mechanical devices that are used to control the
machines with machines. Usually the servo motor is used to control the angular motion
among from 0° to 180° and 0° to 90°. The servo motor working principle based on the
PWM (pulse width modulation) pulses.
A Servo motor is one of the most commonly used motor for precise angular
movement. The advantage of using a servo motor is that the angular position of the
motor can be controlled without any feedback mechanism.
Pulse Width Modulated (PWM) waves are used as control signals and the angular
position is definite by the width of the pulse at the control input. Servo motor having
angle of rotation from 0-180° and angular position can be controlled by varying the duty
cycles among 1ms to 2ms.The control of servo motor connected port0 of 8051
microcontroller. The 11.0592MHz crystal oscillator is used to provide the clock pulsed to
the microcontroller and 22pf ceramic capacitors used to stabilize the operation of
crystal. 10KΩ and 10uf capacitor is used to provide the power on reset to the
microcontroller.
Controlling a Servo Motor with Angle rotations
Servo motor working principle mainly depends upon duty cycles. It uses Pulse Width
Modulated (PWM) waves as control signals. The angle of rotation is resolute by the
pulse width of the control pin.
Servo Motor Working Principle
The servo motor working principle mainly depends upon the „Fleming left hand rule‟.
Basically servo motors are adapted with DC motors, a position sensor, a Gear
reduction, and an electronic circuit. The DC motors achieve powered from a battery and
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run at high speed and low torque. We assembled shaft and gear connected to DC
motors then we can increase and decrease the motor speed gradually.
Fig:Interfacing of servo motor with 8051 Microcontroller
The position sensor senses the location of the shaft from its fixed position and sends
the information to the control circuit. The control circuit decodes the signals accordingly
from the position sensor and compares the actual location of the motors with the
preferred position and accordingly controls the direction of rotation of the DC motor to
get the necessary position. Generally the servo motor requires 4.8V to 6 V DC supply.
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5. Draw the schematic for interfacing a washing machine control with 8051
microcontroller and write8051 ALP for washing machine control. (Nov/Dec 2014)
A washing machine is an electronic device that is designed to wash laundry like clothes,
sheets, towels and other bedding. A washing machine is built with two steel tubs which
are the inner tub and the outer tub whose main role is to prevent water from spilling to
other parts of the machine.
Fig:Interfacing of washing maachine with 8051 Microcontroller
Control knobs in washing machine:
• Load select knob
• Water inlet select knob
• Mode select knob
• Program select knob
Load select knob:- load Number of clothes low medium high Load select
Water inlet select knob:- hot cold both-mixed Water inlet
Mode select knob:- Save mode Normal mode Mode
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Program select knob:- Heavy Clothes very dirty Normal Normal dirty clothes LIGHT
For light dirty clothes Delicate For silk clothes
Machine Operations:-
• Fill:- water will be filled by the pump as per the load knob selected.
• Agitate:- The wash basket will rotate in a clockwise direction for 10 revolutions,
After that basket will stop for 2 seconds, then rotate 10 revolutions in anticlockwise
direction. The process will be continued for specified minutes in cycle table.Drain:- After
agitation, the water and detergent are drained.
Spin:- During spin, agitator will be stationary, only the basket will rotate at
high speed. Then the moisture of clothes are removed through holes in
the inner metallic basket.
Machine Indicators:-
Machine ON
LED ON After completion of washing cycle, buzzer sound will be
generated.
Washing cycle :
Heavy
Normal
Light
Delicate
Washing Machine Drives/Connections:
The drives of the washing machine is connected to 8051 Microcontroller
ports. Hot/Cold Agitator motor drive
Agitator motor drive
Spin motor drive
High level
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Medium level
Low level
Drain
Washing machine ON LED
Heavy
Normal
Light
Delicate
Hot
Normal Buzzer sound Basket
Washing Machine Operation SinalsInput/Output :
The various Operation Signals are connected to microcontroller Input/output Port.
Load / water level select
Water inlet
Program select
Machine ON
Fill water
Agitation control
Output
Spin
Washing complete
Program:Commands for washing-machine controller
SETB LCALL JNB SJMP P2.0
FILL_1 P1.0,LOOP_1 HEAVY Machine ON indication Machine fill with water 1st time
Chkprogsetng knob for heavy.
If P1.0 is not set,jump to LOOP_1
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If P1.0 is set,jump to HEAVY LOOP_1 JNB SJMP P1.1,LOOP_2 NORMAL Check
progsetng knob for normal
If P1.1 is not set.jump to LOOP_2
If P1.1 is set, jump to NORM LOOP_2 JNB SJMP P1.2,LOOP_3 Chckprogsetng knob
for normal.
If P1.2 is not set,jump to LOOP_3
If P1.2 is set,jump to LIGHT LOOP_3 JNB SJMP P1.3,LOOP_4 DELICATE Check prog
set knob for delicate.
If P1.3is not set,jump to LOOP_4 If P1.2 is set,jump to delicate DISPLAY SETB P2.7
Indicate the completion of wash cycle. LOOP_4 NOP LJMP 0000 End of program
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