understanding 8051 with c

8/7/2019 Understanding 8051 with C

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Understanding 8051

By,

Sandip Nair

[email protected]


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Embedded microcontroller

Microcontroller has inbuilt peripherals such as memory,

UART, timers etc where as microprocessor has only theprocessing unit and the peripherals, has to be connected

externally

,

washing machine, digital watch, A/C, automobiles,

microwave oven etc


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Embedded design philosophy

An efficient microcontroller application involves

designing with a minimum external hardware necessary toallow the software to keep up with all of its tasks

An efficient software is easy-to-understand software that


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Understanding 8051

arc tecture


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About 8051

The first device was developed by intel

The architecture had dominated for more than 20 years Other versions are developed keeping the architecture

and instruction set same for low power, larger memory

and with many peripherals added

8051 can be programmed using C, BASIC, C++, forth

and PL/M languages


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Atmel AT89S52

It is a 8-bit microcontroller built on 80C51

architecture

4.0 V to 5.5V operating voltage

It has 8K bytes of ISP flash memory

Three level program memory lock 256 X 8bit internal RAM

32 programmable I/O lines

Three 16 bit timer/counter

Eight interrupt sources Full duplex UART serial channel


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Cont.

Low power idle and power down modes Interrupt recovery from power down

Watch dog timer

Power-off flag

Fast programming time

Flexible ISP programming


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Pin diagram


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Pin description

Pin 40 =VCC = supply voltage 4.0V to 5.5 V

Pin 20 = GND = ground Pin 9 = RST = reset input

Pin 30 =ALE/ PROG = ALE for latching the low byte address

Pin 29 = PSEN =


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Port 0

P0.0 to P0.7 = Pin 39 to Pin 32

Has internal pull up resistor for external program

memory

Low order address/data bus for external program

memory Receives code bytes for flash programming

Outputs code bytes for verification

Requires external pull up register during program

verification


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Port 1

Pin 1 to 8 = P1.0 to 1.7

Has an internal pull up resistor P1.0 = T2 = external count input to timer/counter 2

P1.1 = T2EX = Timer/counter 2 capture/ reload trigger

P1.5 = MOSI = used for in-s stem ro rammin

P1.6 = MISO = used for in-system programming P1.7 = SCK = used for in-system programming


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Port 2

Pin 21 to 28 = P2.0 to 2.7

Has internal pull ups

Used for higher order bus for external memory

Also receives some control signal during flash

programming


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Port 3

Pin 10 to 17 = P3.0 to P3.7

Receives control signals for flash programming andverification

P3.0 = RXD = serial input port

. = =

P3.2 = INT0 = external interrupt 0 = inverted

P3.3 = INT1 = external interrupt 1 = inverted

P3.4 = T0 = timer 0 external input

P3.5 = T1 = timer 1 external input P3.6 = WR = external memory data write strobe = inverted

P3.7 = RD = external memory data read strobe = inverted


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C basics


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C variablesInteger:

It is 16 bit variable type to store integer values

It is default unsigned

Float:

Double is a 64 bit variable type

The calculation with these variable types requires

library function


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C variables

Static and volatile

Constants:

Doesnt vary during the program cycle

It is stored in ro ram memor

#define

used at the top of the program to create short cut to save

typing

Eg, #define uchar unsigned char#define buffersize 100


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Tips for variable

Calculations to be done on signed variable requireslibrary function which adds extra code to the program,

making it lengthy and slow. Thus where ever possible

use unsi ned variable.

Variable naming should be according to the purpose itis used for, such that it helps in understanding the code

for others


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Reference

AT89S52 datasheet

C & the 8051 by Thomas Schultz

understanding 8051 with c

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