EC303 - Chapter 2 LOGIC DESIGN & COMPUTER ARCHITECTUR
description
Transcript of EC303 - Chapter 2 LOGIC DESIGN & COMPUTER ARCHITECTUR
11
LOGIC DESIGN & COMPUTER ARCHITECTURE
LOGIC DESIGN & COMPUTER ARCHITECTURE
222
LOGIC DESIGN & COMPUTER ARCHITECTURE
LOGIC DESIGN & COMPUTER ARCHITECTURE
Sub Topic 2.1: Computer Aided Design
Learning OutcomeAt the end of this presentation, you will be able to:
2.1.1 Define the primary approaches to IC chip designa. Mask-programmable ICsb. Standard-cell devicesc. Custom devicesd. PLD and VHDL
2.1.2 Explain Schematic logic design using CPLDa. Overview of Schematic Design Methodsb. Design Flow Summaryc. Generated Reports after compilation schematic.d. Simulation concept
3
IC DESIGN METHODOLOGY
DESIGN METHODOLOGY TREE DIAGRAM
IC DESIGN METHODOLOGY
STANDARD IC
Standard IC : • Integrated circuits designed and fabricated for
general purpose use.
• Standard IC is available in the market at a very low cost.
• Examples of standard ICs: 74 - SERIES TTL, 4000 - SERIES CMOS, OP-AMP, TIMER, INSTRUMENTATION AMPLIFIER, MEMORY, MICROCONTROLLER, etc.
IC DESIGN METHODOLOGY
EXAMPLES OF STANDARD IC
74-series TTL
4000 series CMOS
Op-Amp Timer
Memory
Microcontroller
IC DESIGN METHODOLOGY
EXAMPLES OF STANDARD IC
IC DESIGN METHODOLOGY
ASICs
• Progress in the fabrication of IC's has enabled the designer to create fast and powerful circuits in smaller and smaller devices.
• This also means that we can pack a lot more of functionality into the same area.
• The biggest application of this ability is found in the design of ASICs.
IC DESIGN METHODOLOGY
ASICs
ASICs stands for : Application Specific Integrated Circuits
• ASICs are IC's that are created for specific purposes - each device is created to do a particular job.
• ASICs are produced for only one or a few customers or applications.
• ASICs are devices made for a specific application such as a mobile phone.
EXAMPLES OF ASICs
IC DESIGN METHODOLOGY
IC DESIGN METHODOLOGYEXAMPLES OF ASICs
GRAPHIC MEDIA ACCELERATOR
GRAPHIC MEDIA ACCELERATOR
SMART CARD CHIPSSMART CARD CHIPS
IC DESIGN METHODOLOGY
IC DESIGN METHODOLOGY
FULL CUSTOM DESIGNAll the circuits and mask layouts are completely
designed for the requirements of a particular IC.
A microprocessor is an example of a full-custom design IC—designers spend many hours squeezing the most out of every last square micron of microprocessor chip space by hand.
IC DESIGN METHODOLOGY
SEMI CUSTOM DESIGN
To make ASICs economic at lower volumes, the semi-custom concept was introduced where many applications share the same basic configuration of logic cells.
The mask layers are customized to fulfill the requirements of a particular IC.
Often used for speedy design with less effort compared to full custom design.
IC DESIGN METHODOLOGY
SEMI CUSTOM DESIGN
There are 3 types of semi custom design:-
1. Gate array (mask-programmable ICs)
2. Standard Cell
3. Programmable Logic Device (PLD)
IC DESIGN METHODOLOGYSEMI CUSTOM IC
GATE ARRAY (mask –programmable ICs)
1. Gate arrays are integrated circuits containing large numbers of digital gates or transistor cells, which can be interconnected in different ways to implement various logic functions.
2. Gate array consists of transistors, usually arranged in two pairs of PMOS and NMOS.
3. ASIC vendors offer a selection of gate array cells, with a different total numbers of transistors on each cell, for example, gate arrays with 50k-, 75k-, and 100k-gates.
IC DESIGN METHODOLOGYSEMI CUSTOM IC
GATE ARRAY FLOOR PLAN
IC DESIGN METHODOLOGYSEMI CUSTOM IC – gate array
Gate array
IC DESIGN METHODOLOGYSEMI CUSTOM IC – gate array
IC DESIGN METHODOLOGYSEMI CUSTOM IC
STANDARD CELL
1. Standard cell design involves the use of pre-designed standard cell @ library cell that has been and stored in database.
2. Standard cell @ library cell consists of simple circuit such as inverter or logic gates (AND, OR, XOR, XNOR, flip-flop), and complex circuit such as register, adder, ROM and RAM.
IC DESIGN METHODOLOGYSEMI CUSTOM IC
STANDARD CELL
3. Design is carried out by simply using the pre-designed cells from the library and then connect the cells so that certain functions can be implemented.
4. To facilitate placement and routing, the standard cells are designed to have equal height but variable widths, so that the final IC layout will have a regular pattern with rows of cells
and interconnect routing running between the rows.
3. Design is carried out by simply using the pre-designed cells from the library and then connect the cells so that certain functions can be implemented.
4. To facilitate placement and routing, the standard cells are designed to have equal height but variable widths, so that the final IC layout will have a regular pattern with rows of cells
and interconnect routing running between the rows.
STANDARD CELL FLOOR PLAN
IC DESIGN METHODOLOGYSEMI CUSTOM IC
I/O Pads
LOGIC BLOCK
BLOCK
Standard Cell
Routing
Standard Cell
Routing
Standard Cell
Routing
Standard Cell
Routing
PROGRAMMABLE LOGIC DEVICE (PLD)
PLD is an array of logic gates that can be programmed by the user which contains functions of a small number of logic circuits in a single chip.
IC DESIGN METHODOLOGYSEMI CUSTOM IC
PROGRAMMABLE LOGIC DEVICE (PLD)
PLD MANUFACTURERS
PROGRAMMABLE LOGIC DEVICE (PLD)
PROGRAMMABLE LOGIC DEVICE (PLD)
GENERAL CHARACTERISTICS OF PLD IC
1. PLD does not require a common mask layout in design.
2. The design time is shorter.
3. It consists of a large block of internal connections that can be a programmed.
4. Programming can be done at different stages: i) at the earliest, it is programmed by the
semiconductor vendor (standard cell, gate array).
ii) by the designer prior to assembly or field deployment.
iii) by the user in circuit.
Programmable logic device as a black box.
Logic gates and
programmableswitches
Inputs
(logic variables) Outputs
(logic functions)
IC DESIGN METHODOLOGYPROGRAMMABLE LOGIC DEVICE
DESIGN METHODOLOGY DIFFERENCES
Design method
Design cost Chip sizeOperation
speedPower
dissipationNo. of mask
Design time
Full custom
The most expensive
The smallest
Highest speed
5x Smaller
Numerous
Time-consumi
ng
Standard cell
Average Small High-speed3x
smallerMany Average
Gate array
Cheaper Large Slow2x
Smaller1@2 piece
Fast
PLDThe
CheapestLargest Slowest
1x Smaller
NoneThe
fastest
IC DESIGN METHODOLOGY
PLD programming
• Schematic Entry• Text-Based Entry
VHDL
• VHDL is the VHSIC Hardware Description Language.
• VHSIC is an abbreviation for Very High Speed Integrated Circuit
• a language to describe the structure and behaviour of digital electronic hardware designs, such as ASICs and FPGAs as well as conventional digital circuits.
D Flip-flop Model
Bit values are enclosed in single quotes
Design Entry Techniques
• Schematic – Designer draws the equivalent design using gates and other logic circuits (can include IC’s such as JK FF or 74xxx parts)
• Waveform – Design draws the desired input and output waveforms for the device
• Text Design Files – Design specifies the design using a design language such as Altera Hardware Design Language (AHDL)
Example of Schematic Design
Example of Waveform Design
Learning OutcomeAt the end of this presentation, you will be able to:
2.2 Realize element logic in computer logic
2.2.1 Define clocking in terms of a digital computer. 2.2.2 Explain function clocks (wave form) in digital computer. 2.2.3 Explain gated flip-flop: a. SR flip-flop b. D flip-flop c. Master-slave flip-flop d. JK flip-flop 2.2.4 Use schematic CPLD to simulate digital output for above flip-flop.
35
Element Logic in Computer Logic
37
Introduction
• Latch is a type of temporary storage device that has two stable states (bistable).
• Latches and Flip-flops are used in sequential circuits.• Differences between sequential circuits and
combinational circuits.
38
Introduction
• Latch is normally placed in a category separate from that flip – flops.
• The main difference between latch and FF is in the method used for changing their state.
• Term synchronous means that the output changes state only at a specified point on the triggering input called the clock (CLK).
Logic circuits are classified into two groups:
Combinational logic circuits
Sequential logic circuits
Basic buildingblocks include:
Basic building blocksinclude FLIP-FLOPS:
Element Logic in Computer Logic
Logic gates make decisions
Flip Flops have memory
FLIP-FLOPS• Flip-flops are memory elements that change state on clock signals.
• Memory elements capable of storing one bit
• Flip Flops are wired to form counters, shift registers, and various memory devices.
command Memory element stored value
Q
clock
41
Edge – Triggered Flip - Flops
• Change state either at the positive edge (rising edge) or at the negative edge (falling edge) of the clock pulse.
• Sensitive to its inputs only at this transition of the clock.
• Three types of edge triggered FF1. SR 2. D3. T4. JK
42
Edge – Triggered Flip – FlopsLogic Symbols
43
Positive edges Negative edges
Positive pulses
CLOCK SIGNAL The clock signal is generally a rectangular pulse train or square wave, as shown below :
• Circuits in computers are “clocked”• At each clock rising (or falling) edge, some specified actions are done,
usually within the next rising (or falling) edge
TRIGGERING OF FLIP-FLOPS
• Level-triggering is the transfer of data from input to output of a flip-flop anytime the clock pulse is proper voltage level.
45
SR FFLogic Symbols
46
SR FFTruth Table
Inputs OutputsComments
S R CLK Q Q
0 0 X Qo Qo No change
0 1 0 1 RESET
1 0 1 0 SET
1 1 ? ? Invalid condition
= clock transition LOW to HIGH
X = Irrelevant (“don’t care”)
Qo = output level prior to clock transition
47
SR FFExample
48
D FF
• D flip – flop is useful when a single data bit (1 or 0) is to be stored.
• The addition of an inverter to an S – R flip flop creates a basic D flip – flop.
49
D FFTruth Table
Inputs OutputsComments
S CLK Q Q
1 1 0 SET (stores a 1)
0 0 1 RESET (stores a 0)
= clock transition LOW to HIGH
50
D FFExample
51
• Versatile and is widely used type flip – flop.• The difference between J – K and S – R is that J – K flip – flop
has no invalid state as does S – R flip – flop.
JK FF
52
• Transitions illustrating the toggle operation when J = 1 and K = 1.
JK FF
53
JK FFTruth Table
Inputs OutputsComments
J K CLK Q Q
0 0 Qo Qo No change
0 1 0 1 RESET
1 0 1 0 SET
1 1 Qo Qo Toggle
= clock transition LOW to HIGH
Qo = output level prior to clock transition
54
JK FFExample
55
Asynchronous Preset and Clear Inputs
• Independent of the clock.• Active level on the preset input will set the flip – flop.• Active level on the clear input will reset it.
Note : for synchronous operation, both preset and clear inputs must
both kept HIGH.
56
Asynchronous Preset and Clear InputsLogic Diagram
57
Asynchronous Preset and Clear InputsExample
58
Master – Slave Flip – Flops
• Data are entered into the flip flop at the leading edge of the clock pulses, but the output does not reflect the input state until the trailing edge.
• Pulse – triggered master – slave flip – flop does not allow data to change while the clock pulse is active.
59
Pulse – Triggered Master – Slave Flip – Flops
Master Slave JK Flip-flop
60
• Composed of two sections, the master section and the slave section.
• A master section is basically a gated latch.• The slave section is the same except that it is clocked on the
inverted clock pulse and is controlled by the outputs of the master section rather than by the external J – K inputs.
Pulse – Triggered Master – Slave Flip – Flops
61
Pulse – Triggered Master – Slave Flip – Flops – Truth Table
Inputs OutputsComments
J K CLK Q Q
0 0 Qo Qo No change
0 1 0 1 RESET
1 0 1 0 SET
0 1 Qo Qo Toggle
= clock transition LOW to HIGH
Qo = output level prior to clock transition
62
Pulse – Triggered Master – Slave Flip – Flops – Logic Symbol
Learning OutcomeAt the end of this presentation, you will be able to:
2.3 Realize flip-flop application
2.3.1 Explain Shift Register operation. 2.3.2 Design Shift Register using flip-flop JK. 2.3.3 Determine kinds of binary counter 2.3.4 Explain binary counter operation using: a. Flip-flop SR b. Flip-flop JK 2.3.5 Design a sequence counter (3 bit) 2.3.6 Design sequential magnitude comparator 2.3.7 Design BCD to seven segment decoder
63
64
Flip-Flop Applications• Applications of Flip-Flop:-
– Counters• Asynchronous Counter
• Synchronous Counter
– Register
65
Shift Register Shift registers are constructed using several flip-
flop, connected in such a way to STORE and TRANSFER digital data.
Basically, D flip-flop is used. The input data (either ‘0’ or ‘1’) is applied to the D terminal and the data will be stored at Q during positive/negative-edge transition of the clock pulse.
D Q
Q
1 1
positive edge transition of CLK
66
One D FF is used to store 1-bit of data. Thus, the number of flip-flops used is the same with the number of bit stored.
Shift register mean that the data in each FF can be transferred/move to other FF upon edge triggering of the clock signal.
Four types of data movement in shift register are:-
Parallel in / parallel out (PIPO)
Serial in / serial out (SISO)
Parallel in / serial out (PISO)
Serial in / parallel out (SIPO)
Shift Register
67
Serial Data VS Parallel Data movement
Serial Parallel
•Movement of N-bit data require N number of CLK pulses. Thus, the operation is slow.
•Only one FF is required to be connected at the output terminal, thus only one wire is required.
•Require only one CLK pulse to transfer all N-bit of data. Thus, operation is faster than serial.
•Required N number of connection to the output terminal, which is proportional to the number of bit. Thus, too many connection is required.
Shift Register
68
Parallel in / parallel out (PIPO) Flip-flop configuration for PIPO register.
D Q2
CP
D Q1
CP
D Q3
CP
D Q0
CP
CLK
D3 D2 D1 D0
Q3 Q2 Q1 Q0
69
PIPO data movement.
Q3
Q2
CLK
Q1
Q0
1 0 1 1 1
0
0
0
0
1 0 10 0
0
0
1 1 1 1
0 0 1 0
D3
D2
D1
D0
1
0
1
0
0
1
1
0
Parallel in / parallel out (PIPO)
70
Serial in / serial out (SISO) Flip-flop connection for SISO.
D Q1
FF1
CP
D Q2
FF2
CP
D Q0
FF0
CP
D Q3
FF3
CPCLK
DIN
1st CLK 2nd CLK 3rd CLK 4th CLK
71
SISO data movement. Binary data 10111 is transferred!
DATA-IN
Q0
Q1
1st
CLK
2nd 3rd 4th 5th
Q2
Q3
Serial in / serial out (SISO)
1 0 1 1 1
72
Flip-flop connection for SIPO.
D Q1
FF1
CP
D Q2
FF2
CP
D Q0
FF0
CP
D Q3
FF3
CPCLK
DIN
1st CLK 2nd CLK 3rd CLK 4th CLK
Serial in / parallel out (SIPO)
Q0 Q1 Q2 Q3
73
SIPO data movement. Binary data 10111 is transferred!
DATA-IN
Q0
Q1
1st
CLK
2nd 3rd 4th 5th
Q2
Q3
Serial in / parallel out (SIPO)
1 0 1 1 1
1
1
0
1
74
Flip-flop connection for PISO.
Parallel in / serial out (PISO)
D Q1
FF1
CP
D Q2
FF2
CP
D Q0
FF0
CP
D Q3
FF3
CPCLK
D0 D1 D2 D3SHIFT/LOAD
Serial data out
75
PISO data movement.
SHIFT/LOAD
CLK
Q3
0
0 1 1 1
1 0 1
0
0
0
1
1 1 1 1
0 0 1 1
D0
D1
D2
D3
1 0
Parallel in / serial out (PISO)
0 1 0 1
76
A shift register counter is a shift register whose output being fed back (connected back) to the serial input. This shift register would count the state in a unique sequence!
Two types of shift register counter:-
The ring counter
The Johnson counter
Shift Register Counters
77
Ring Counter
Q3 Q2 Q1 Q0
78
Ring Counter (continue)
0 0 0 1
1 0 0 0
0 1 0 0
0 0 1 0
79
Ring Counter (continue)
80
Ring Counter (continue)
Ring counters are used to construct “One-Hot” countersIt can be constructed for any
desired MOD numberA MOD-N ring counter uses N flip-flops connected in the
arrangement as shown in fig. a)In general ring-counter will
require more flip-flops than a binary counter for the same
MOD number
81
Ring Counter (continue)
82
Johnson Counter Or Twisted-ring counter
Johnson counter constructed exactly like a normal ring counter except that the inverted output of the last flip-flop is fed back to
first flip-flop
83
Johnson Counter (Continue)
A
B
C
0 1 1 1
0 0 1 1
0 0 0 1
84
Johnson Counter (Continue)
85
Chips for shift registers
• 74164 is a 8-bit SIPO shift register
74164
CLK
CLR
AB
Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7
86
Chips for shift registers
• 74165 is a 8-bit PISO register
74165
CLK
CLK INH
SH/LDSER
D0 D1 D2 D3 D4 D5 D6 D7
Q7
Q7
87
Chips for shift registers
• 74195 can be used as a 4-bit PIPO register
74195
CLK
SH/LD
JK
Q0 Q1 Q2 Q3
CLR
D0 D1 D2 D3
88
Chips for shift registers
• 74194 is a 4-bit universal bidirectional shift register
74194
CLK
SR SER
CLRS0
S1
Q0 Q1 Q2 Q3
SL SER
D0 D1 D2 D3
89
Counters• A counter is a register that goes through a
predetermined sequence of states upon the application of clock pulses.– Asynchronous counters – Synchronous counters
• Async. counters (or ripple counters)– the clock signal (CLK) is only used to clock the first FF.
– Each FF (except the first FF) is clocked by the preceding FF.
• Sync. counters, – the clock signal (CLK) is applied to all FF, which means that all
FF shares the same clock signal,
– thus the output will change at the same time.
90
Flip-Flop Applications• Applications of Flip-Flop:-
– Counters• Asynchronous Counter
• Synchronous Counter
91
Asynchronous counters• Modulus (MOD) – the number of states it counts
in a complete cycle before it goes back to the initial state.
• Thus, the number of flip-flops used depends on the MOD of the counter (ie; MOD-4 use 2 FF (2-bit), MOD-8 use 3 FF (3-bit), etc..)
• Example: MOD-4 ripple/asynchronous up-counter.
92
Asynchronous Counters (continue)
• The asynchronous counter that counts 4 number starts from 00011011 and back to 00 is called MOD-4 ripple (asynchronous) up-counter.
• Next state table and state diagram Present State Next State
Q1Q0 Q1Q0
00 01
01 10
10 11
11 00
00
01
10
11
93
• MOD-4 Asynchronous up-counter
J Q
K Q
CLK
1 J Q
K Q
CLK
1
Q0 (LSB) Q1 (MSB)
CLKQ1 0 0 1 1 0 0 1 1 0
Q0 0 1 0 1 0 1 0 1 0
Binary 0 1 2 3 0 1 2 3 0
Asynchronous Counters (continue)
CLK
94
• MOD-8 Asynchronous up-counter
J Q
K Q
CLK
1 J Q
K Q
CLK
1 J Q
K Q
CLK
1
C B A
A 0
B 0
C 0
CLK
Asynchronous Counters (continue)
95
• Next state table and state diagramPresent
StateNext State
ABC ABC000 001001 010010 011011 100100 101101 110110 111111 000
0
1
2
3
7
6
5
4
Asynchronous Counters (continue)
96
• Exercise:– Design a MOD-16 ripple up-counter
– Design a MOD-4 ripple down-counter
– Design a MOD-8 ripple down counter
– Design a MOD-16 ripple down counter
Asynchronous Counters (continue)
97
• 2-bit Asynchronous down counter
J Q
K Q
CLK
1 J Q
K Q
CLK
1
B (LSB) A (MSB)
CLKB 0 1 0 1 0 1 0 1 0
A 0 1 1 0 0 1 1 0 0
Binary 0 3 2 1 0 3 2 1 0
Asynchronous Counters (continue)
CLK
98
• So far, we have design the counters with MOD number equal to 2N, where N is the number of bit (N = 1,2,3,4….) (also correspond to number of FF)
• Thus, the counters are limited on for counting MOD-2, MOD4, MOD-8, MOD-16 etc..
• The question is how to design a MOD-5, MOD-6, MOD-7, MOD-9 which is not a MOD-2N (MOD 2N) ?
• MOD-6 counters will count from 010 (0002) to 510(1012) and after that will recount back to 010 (0002) continuously.
Asynchronous Counters (continue)
99
Asynchronous Counters• MOD-6 ripple up-counter (MOD 2N)Present
St.Next St.
ABC ABC000 001001 010010 011011 100100 101101 000(110)
01
23
5
4
Reset the state to 0002 when 1102 is detected
100
Asynchronous Counters (continue)
• Circuit diagram for MOD-6 ripple up-counter (MOD 2N)
J Q
K CLR
Q
CLK
1 1 1
C B A
J Q
K CLR
Q
CLK
J Q
K CLR
Q
CLK
Detect the output atABC=110 to activate
CLR. NAND gate is used to detect outputs that generates ‘1’!
CLK
101
Chip for Asynchronous counters
• 74293 IC for Asynchronous counter with Reset (MR1 and MR2) MR1
MR2Q0Q1Q2Q3
CP0
CP174293
J Q
K
CLR Q
CLK
1 1 1
Q0 Q1 Q2
J Q
K
CLR Q
CLK
J Q
K CLR
QCLK
1 J Q
K
CLR Q
CLK
Q3
MR1MR2
CP0
CP1
102
Chip for Asynchronous counters (continue)
• Using 74293 IC to design MOD 16 asynchronous up-counter!
• Exercise: – use 74293 IC to design MOD-10 ripple up-counter
MR1
MR2
Q0Q1Q2Q3
CP0
CP174293
1 0 1 0
103
Chip for Asynchronous counters (continue)
• Exercise:
– Determine the MOD for each configuration shown below?
MR1
MR2
Q0Q1Q2Q3
CP0
CP174293
MR1
MR2
Q0Q1Q2Q3
CP0
CP174293
1 0 1
104
Chip for Asynchronous counters (continue)
• Determine the MOD for each configuration shown below? MR1
MR2
Q0Q1Q2Q3
CP0
CP174293
105
Asynchronous counters• Disadvantages of Asynchronous Counters:-
– Propagation delay is severe for larger MOD of counters, especially at the MSB.
– Existence of ‘glitch’ is inevitable for MOD 2N counters.
– Difficult to design random counters (i.e:- to design circuit that counts numbers in these sequence 56723156723156….)
• Solution, use SYNCHRONOUS COUNTERS.
106
Synchronous counters• For synchronous counters, all the flip-flops are using the
same CLOCK signal. Thus, the output would change synchronously.
• Procedure to design synchronous counter are as follows:-STEP 1: Obtain the State Diagram. STEP 2: Obtain the Excitation Table using state
transition table for any particular FF (JK or D). Determine number of FF used.
STEP 3: Obtain and simplify the function of each FF input using K-Map.
STEP 4: Draw the circuit.
107
Synchronous counters• Design a MOD-4 synchronous up-counter, using JK FF.
STEP 1: Obtain the State transition Diagram
0
1
2
3
00
01
10
11Binary
108
Synchronous countersSTEP 2: Obtain the Excitation table. Two JK FF are
used.
Present State Next State
A B A B JA KA JB KB
0 0 0 1 0 X 1 X
0 1 1 0 1 X X 1
1 0 1 1 X 0 1 X
1 1 0 0 X 1 X 1
OUTPUT TRANSITIONQN QN+1
FF INPUTJ K
0 0 0 X0 1 1 X1 0 X 11 1 X 0Excitation table
109
Synchronous countersSTEP 3: Obtain the simplified function using K-Map
BA 0 1
0 0 1
1 X X
JA = B
BA 0 1
0 X X
1 0 1
KA = B
BA 0 1
0 1 X
1 1 X
JB = 1
BA 0 1
0 X 1
1 X 1
KB = 1
110
Synchronous countersSTEP 4: Draw the circuit diagram
JB Q
KB Q
CLK
1JA Q
KA Q
CLK
B (LSB) A (MSB)
111
Synchronous counters• Exercise:-
– Design MOD-4 sync up-counter using D flip-flop.
– Design MOD-8 sync up-counter using D flip-flop.
– Design MOD-8 sync up-counter. Use T FF for MSB, D FF for second bit and JK FF for LSB.
– Design MOD-16 sync up-counter using T flip-flop.
112
Synchronous counters• Design a MOD-4 synchronous down-counter, using JK
FF?
STEP 1: Obtain the State transition Diagram
0
3
2
1
00
11
10
01Binary
113
Synchronous counters– Obtain the Excitation table. Two JK FF are used.
Present St.
Next St.
A B A B JA KA JB KB
0 0
0 1
1 0
1 1
OUTPUT TRANSITIONQN QN+1
FF INPUTJ K
0 0 0 X0 1 1 X1 0 X 11 1 X 0
114
Synchronous counters– Obtain the simplified function using K-Map
BA 0 1
0
1
JA =
BA 0 1
0
1
KA =
BA 0 1
0
1
JB =
BA 0 1
0
1
KB =
115
Synchronous counters– Draw the circuit diagram
JB Q
KB Q
CLK
JA Q
KA Q
CLK
B
A
116
Synchronous counters• Exercise:-
– Design MOD-4 sync down-counter using D flip-flop.
– Design MOD-8 sync down-counter using D flip-flop.
– Design MOD-8 sync down-counter. Use T FF for MSB, D FF for second bit and JK FF for LSB.
– Design MOD-16 sync down-counter using T flip-flop.
117
Chip for synchronous counter 74163
74163
CLR
LOADENTENPCLK
D0 D1 D2 D3
Q0 Q1 Q2 Q3
RCO