Engr433 : Digital Designcurt.nelson/engr433... · Engr354 -Registers and Counters 4 Shift Registers...
14
Engr354 - Registers and Counters 1 Engr433 : Digital Design Registers and Counters Curtis Nelson Overview • In this presentation we cover: – Registers, which store multiple bits; – Shift registers, which shift the contents of registers; – Counters of various types.
Transcript of Engr433 : Digital Designcurt.nelson/engr433... · Engr354 -Registers and Counters 4 Shift Registers...
Engr354 - Registers and Counters 1
Engr433 : Digital Design
Registers and Counters
Curtis Nelson
Overview
• In this presentation we cover:– Registers, which store multiple bits;– Shift registers, which shift the contents of registers;– Counters of various types.
Engr354 - Registers and Counters 2
Review - Sequential Circuits
• Combinational – outputs depends only on the inputs;• Sequential – output depends on input and past behavior:
– Requires use of storage elements;– Content of the storage elements is called state;– Circuit goes through a sequence of states as a result of changes in
inputs.
• Synchronous – Controlled by a clock;• Asynchronous – No central clock.
Latches and Flip-Flops
Engr354 - Registers and Counters 3
Multibit Registers and Latches
74x374 8-bit Register
Engr354 - Registers and Counters 4
Shift Registers
• A shift register is an n-bit register with a provision for shifting stored data by one bit position at each tick of the clock.
Shift Registers – Serial-in, Parallel-out
Engr354 - Registers and Counters 5
74x194 4-bit Universal Shift Register
74x194 4-bit Universal Shift Register
Engr354 - Registers and Counters 6
74x194 4-bit Universal Shift Register
74x194 4-bit Universal Shift Register
Engr354 - Registers and Counters 7
Counters
• Counter – generally used for any clocked sequential circuit whose state diagram contains a single cycle;
• Modulus – the number of states in the cycle;• A counter with m states is called a modulus-m counter or a divide-by-m counter;
• Ripple counters (rare due to delays);• Synchronous counters (common):
⎯ Connects all of its flip-flop clock inputs to the same common CLK signal so that all flip-flop outputs change at the same time.
Synchronous 4-bit Binary Counter – 74x163
Engr354 - Registers and Counters 8
Synchronous 4-bit Binary Counter – 74x163
Synchronous 4-bit Binary Counter – 74x163
Engr354 - Registers and Counters 9
Synchronous 4-bit Binary Counter – 74x169
D Q
Q
Clock
D Q
Q
D Q
Q
Start
Q 0 Q 1 Q n 1 “
Clock
Q 0
Start
Two-bit up-counter
w 0 En
y 0
w 1
y 1 y 2 y 3
1
Q 1 Q 2 Q 3
2-to-4 decoder
Q 1 Q 0
(a) An n -bit ring counter
Clock
Clear
(b) A four-bit ring counter
Ring Counter
Engr354 - Registers and Counters 10
D Q
Q
Clock
D Q
Q
D Q
Q
Q 0 Q 1 Q n 1 –
Reset
Johnson Counter
T Q
Q Clock
T Q
Q
T Q
Q
1
Q 0 Q 1 Q 2
(a) Circuit
Clock
Q 0
Q 1
Q 2
Count 0 1 2 3 4 5 6 7 0
(b) Timing diagram
Three-Bit Up-Counter
Engr354 - Registers and Counters 11
T Q
Q Clock
T Q
Q
T Q
Q
1
Q 0 Q 1 Q 2
(a) Circuit
Clock
Q 0
Q 1
Q 2
Count 0 7 6 5 4 3 2 1 0
(b) Timing diagram
Three-bit Down-Counter
T Q
Q Clock
T Q
Q
T Q
Q
1 Q 0 Q 1 Q 2
(a) Circuit
Clock
Q 0
Q 1
Q 2
Count 0 1 2 3 5 9 12 14 0
(b) Timing diagram
T Q
Q
Q 3
Q 3
4 6 8 7 10 11 13 15 1
Four-bit Synchronous Up-Counter
Engr354 - Registers and Counters 12
T Q
Q Clock
T Q
Q
Enable
Clear
T Q
Q
T Q
Q
Inclusion of Enable and Clear Capability
EnableQ 0 Q 1 Q 2
D 0 D 1 D 2 LoadClock
1 0 0 0
Clock
0 1 2 3 4 5 0 1
Clock
Count
Q 0
Q 1
Q 2
(a) Circuit
(b) Timing diagram
Modulo-6 Counter with Synchronous Reset
Engr354 - Registers and Counters 13
T Q
Q Clock
T Q
Q
T Q
Q
1 Q 0 Q 1 Q 2
(a) Circuit
Clock
Q 0
Q 1
Q 2
Count
(b) Timing diagram
0 1 2 3 4 5 0 1 2
Modulo-6 Counter with Asynchronous Reset
EnableQ0Q1Q2
D0D1D2
LoadClock
1000
Clock
Q30 D3
EnableQ0Q1Q2
D0D1D2
LoadClock
000
Q30 D3
BCD0
BCD1
Clear
A Two-digit BCD Counter
Engr354 - Registers and Counters 14
Summary
• In this presentation we covered:– Registers, which store multiple bits;– Shift registers, which shifts the contents of registers;– Counters of various types.
