digital systems ii: intro beginnings j. schmalzel r. polikar
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Digital Systems II: IntroBeginnings
J. Schmalzel
R. Polikar
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Digital Foundations
The basic model of a computer system:
CPU MEM
I/O
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Central Processing Unit (CPU)
ControlsExecutesComputes (Fixed- and/or Floating-
Point)
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Memory
Program storeData storageHigh-speedLow-speedVolatile, Non-volatile
RAM, ROM, FLASH (EEPROM)
FastSlow
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Input/Output (I/O)
Communication between CPU and outside world
FastSlowStandardized (e.g., IEEE 802.11b)Parallel (IEEE 1184)Serial (USB
2.0)
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Hierarchical View of EP and Digital Systems
CPU MEM
I/O
GatesBoolean Algebra
Design Techniques
MSI Functions
State Machines
Interface Method
Computer Architecture
Operating System
HLLs
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Sequential Circuits Include feedback Presence of a clock Behavior is no longer simply a function of
the inputs--must be evaluated synchronously with clock
Flip-flops D-type J-K type etc.
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CK
QD
D-F/F
Excitation Function: Dn = Qn+1
Q*
P
C
P C Dn Qn+1
1
0 1 X
1 1 1
1 0 X
1 1 0
0 0 X
1
0
Illegal0
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Xilinx F/F’s
FDC: D-F/F w/ asynchronous clear
FDS: D-F/F w/ synchronous set
The FDS will not set upon activation of the set input without also activating clock
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State Machines
Mealy: Outputs depend on states and on inputs.
Moore: Outputs depend only on states. One-Hot: A type of Moore machine in
which there is one F/F per state.
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State Machine Models
(& One-Hot)
Inputs
State Memory
Combinatorial Network
Clk
Moore Outputs
Mealy Outputs
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Sequential Circuit Design
Problem statement State diagram Transition table Simplified excitation functions Implementation Verification
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Example
Design a sequence detector that will identify 1011.
SM1011 Z
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State Diagram
Input
Input
Input/Output
Input/Output
Name
OutputName
Moore Mealy
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One-Hot SMs
Moore machines are glitchless since outputs change only synchronously with clock.
For relatively small numbers of states, techniques of F/F minimization are largely counterproductive with available “sea-of-gates” FPGA. A 12-state SM: Don’t bother to reduce/encode. A 16-bit counter: Definitely encode states.
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SM for 1011 Sequence DetectorReset
Found1
Found2
Found3
Found4
Z
Found
None
1
0
0
11
1
0
0
0
1
Note: Dashed lines show non-resetting algorithm.
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Transition TableOutput Present State Input Next State
Z F0 F1 F2 F3 F4 X F0’ F1’ F2’ F3’ F4’ 0 1 0 0 0 0 0 1 0 0 0 0
1 0 1 0 0 0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 0 0 1 0 0 0 0 1 0 0 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0
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Excitation FunctionsThe Transition Table could be large: 26 = 64, but since this is a One-Hot SM, there can be only one state active at a time. When writing the BA for each excitation function, listing the complemented states is redundant.
For example: DF0 = F0•X* + F2•X*, instead of
DF0 = F0•F1*•F2*•F3*•F4*•X* + F0*•F1*•F2•F3*•F4*• X*
Similarly,
DF1 = F0•X + F1•X + F4•X
DF2 = F1•X* + F3•X* + F4•X*
DF3 = F2•X
DF4 = F3•X
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Simplification
If there are any redundant terms, can simplify; however, for One-Hot approach, there are no simplifications possible since must account for every separate state path.
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ImplementationAssign one D-F/F per state and complete the combinatorial network required for each input. Implementation of F0 is shown:
Clk
&
&+ D Q F0
F0
F2
X*
X*
The final network output, Z = F4. For reset, use asynchronous F/F inputs: Preset F0 and clear F1-F4.
P
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Verification
Check that the SM performs as required.
More complex input vectors are required since the internal state memory expands total possible states.
Use simulation tools.
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The Power of One-Hot Design
Can skip transition table--“read” the implementation directly off the state diagram:
Found11
1
Found
None
Clk
&
&+ D Q F1
F0
F1
X
X C
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Sequential Circuit Functions
Counters Binary, BCD Ripple, Synchronous
Registers and Latches PIPO, PISO, SIPO, SISO
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In-Class Lab
Refer to EP Schematic 090-0016 What is the function of U5? Explain how it operates--what is the address
of LED3? How does it drive the LEDs? What currents are supplied (in or out) by
the 74HC259 to light up the LEDs?
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In-Class Lab What is the function of U5? Addressable latch to control
annunciators.
Explain how it operates--what is the address of LED3? An I/O write to address (CS1+2) enables the D-F/F, Q2.
How does it drive the LEDs? A logic 1 output forward-biases the LEDs, turning them on. The current-limiting resistors prevent excessive forward current. Assuming Vf of the LED is approx. 1.7 V, the current through the diode would be about (4.3-1.7)V/470 = 5.5 mA (which is nearly one of the specified load currents!). When an output is a logic 0, the associated LED is zero biased, which won’t turn it on.
What currents are supplied (in or out) by the 74HC259 to light up the LEDs?
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Digital v. Analog Electronics
Digital: Concerned with (usually) only two logic levels. Uses saturating logic circuits. For example, “1” = 5.0, “0” = 0.0
Analog: Concerned with potentially infinite number of values between two extremes. For example, 0.0 < V < 5.0.
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In-Class Lab
ESD Principles Brief tour of Z-World Core Module Assembly notes Software notes Demo
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ESD Principles
Minimize electrostatic charge generationNeutralize chargesDrain off chargesMinimize electrostatic fields and discharge effectsProtect ESD-sensitive devices during handling and
transport
Treat every device as if it were ESD sensitive!
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Electrical Model of ESD Field Equipment
Probe
Snap (Wrist) Snap (Mat)1 M 1 M
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Assembly Notes
Objective is to add headers and other components to add test points and features.
Good construction practices.Good soldering practices.
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Introduction to Embedded Processors
Into the model of an embedded computer system:
CPU MEM
I/O
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Introduction to Embedded Processors: User v. Developer User
Transparent product/performance Low-cost Excellent interaction design
Developer Meet schedule and budget (Reuse earlier S/W and
H/W--finish project w/o forgoing sleep) Meet marketing’s specifications Do it better than the last time
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Digital Foundations: The Architecture of an EP
The basic model of a computer system:
CPU MEM
I/O
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The Bus-Oriented EP
CPU MEMI/O
Add
Data
Con
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Bus BasicsNeed to provide a shared medium that prevents contention. Use of these methods provides a way to provide bidirectional signal paths. Of course, does require arbitration.
Tri-State: “1” “0” and “High-Z”
Open-Collector (Drain): Passively pulled high (“1”) or actively pulled low (“0”)
A Y
E A E Y0 1 01 1 1X 0 Z
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Example EP Feature List
Small footprint 25.8 MHz CPU 40 CMOS-compatible
parallel I/O lines Four CMOS-compatible
serial ports; max async rate of 806 kbps, max sync rate of 6.45 Mbps
8-bit data bus 13 address lines
Control signals (I/O read, write)
Master/slave config Reset input, output 5, 8-bit and 2, 10-bit
timers 256K flash EPROM,
512KB SRAM RTC Status, WDT outputs
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Questions, Comments, Discussion