Counters and Shift Registers

1
Counters and Shift Registers

• ELEC 311
• Digital Logic and Circuits
• Dr. Ron Hayne
• Images Courtesy of John Wakerly and Prentice-Hall

2
T Flip-Flop

• T (toggle) flip-flop
• Changes state every positive clock edge

3
(Asynchronous) Ripple Counter

• Q3 Q2 Q1 Q0
• 0 0 0 0
• 0 0 0 1
• 0 0 1 0
• 0 0 1 1
• 0 1 0 0
• 0 1 0 1
• 0 1 1 0
• 0 1 1 1
• 1 0 0 0

. . .
4
Synchronous (Serial) Counter

• Serial enable logic

5
Synchronous (Parallel) Counter

• Parallel enable logic

6
74x163 4-bit Binary Counter

• Synchronous
• Active-low Load
• Active-low Clear
• Two Enables
• ENP (parallel)
• ENT
• Ripple Carry Out
• RCO (ENT)
• Cascading

7
74x163 4-bit Binary Counter
8
Changing Counting Modulus
1000, 1001, 0000, 0001,
9
VHDL Counter
10
VHDL Counter
11
(Shift) Registers

• Flip-flops packaged in sets
• Quad register gt 4 D flip-flops with common clock
• CLR_L gt async, active-low, clear signal
• Types
• Serial-in, Serial-out
• Serial-in, Parallel-out
• Parallel-in, Serial-out
• Parallel-in, Parallel-out

12
Quad Register

• Parallel-in, Parallel-out (no shift)

13
Serial-In, Serial-Out
14
Serial-In, Parallel-Out
RIN
15
Parallel-In, Serial-out
QD
16
74x194 Universal Shift Register
17
Universal Shift Register
18
(Simple) Ring Counter

• n-bit Shift Register
• n State Counter

19
Ring Counter
20
(Simple) Ring Counter
21
Self-Correcting Ring Counter
22
VHDL Shift Register
23
VHDL Shift Register
24
VHDL Shift Register
25
Summary

• Counters
• Asynchronous
• Synchronous
• Shift Registers
• Serial, Parallel, Universal
• Ring Counters