Shift registers

1. Shift Registers

2.  A shift register is a sequential logic block
made up of flip-flops that allows parallel or
serial loading and serial or parallel outputs
as well as shifting bit by bit.
 Common tasks of shift registers:
– Serial/parallel data conversion
– UART (an example)
– Time delay
– Ring counter
– Twisted-ring counter or Johnson counter
– Memory device
Shift Registers

3. 3684
Shift Registers
368
36
3
An example of a shift
register at work would
be a calculator.

4. 1 0 1 0 1 1 0 1
Serial In Serial out
…0 1… …1 0…
Serial In
1 0 1 0 1 1 0 1
1 0 1 0 1 1 0 1
…0 1…
Parallel out
MSB LSB
1 0 1 0 1 1 0 1
1 0 1 0 1 1 0 1
Parallel out
Parallel in
MSB LSB
1 0 1 0 1 1 0 1
1 0 1 0 1 1 0 1
Parallel In
MSB LSB
Serial Out
…1 0…
Shift Register Types

7. SERIAL LOAD SHIFT REGISTER
Note the use of D FFs.
Clock (CLK) inputs wired in parallel.
Clear (CLR) inputs can be activated with LOW
or disabled with HIGH.
Preset (PS) inputs deactivated.
Parallel outputs here.
Order= A B C D
Inputs here:
(1) Data
(2) Clock
(3) Clear
Clear input:
Active = 0
Deactivated = 1
Clock input:
Positive-edge
triggering
Clock Pulse 1
Clear = 0
Data = 1
0 0 0 0
1 0 0 0
Clock Pulse 2
Clear = 1
Data = 1
1 1 0 0
0 1 1 0
Clock Pulse 3
Clear = 1
Data = 1
Clock Pulse 4
Clear = 1
Data = 0
0 0 1 1
Clock Pulse 5
Clear = 1
Data = 0
0 0 0 1
Clock Pulse 6
Clear = 1
Data = 0
Clock Pulse 7
Clear = 1
Data = 1
1 0 0 0
0 1 0 0
Clock Pulse 8
Clear = 1
Data = 0 4-bit
serial-in
parallel out
shift right
shift register

18. 74164 IC Shift Register
74LS164
Dsa
Dsb
CP
MR
Q7
Q6
Q5
Q4
Q3
Q2
Q1
Q0
Serial In Parallel out
Clock
Master reset