Transcript Chapter - 06 (II) - 3rd Semester Notes

Lect# 9 Register (Continued)
Register
• A register is a sequential circuit that
can be set to a specific state and retain
that state until externally changed.
–State is a combination of bits
1
Register Design
• An S-R latch is a simple 1-bit register.
–With (S)et input, latch output can be
set to 1
–With (R)eset input, latch output can
be set to 0.
2
Register Design
• A D flip-flop can be used as a 1-bit register
– Input 0, output is set to 0 when flip-flop is
clocked
– Input 1, output is set to 1 when flip-flop
clocked
– Can consider the clock to be a load signal.
– On rising edge of load signal, the data on D
input line is stored in the flip-flop
3
Multibit Register
• Use multiple flip-flops. Each stores a single bit.
• Common load signal.
d
c
Dd
Ck Qd
load
d
b
a
inputs
Dc
Db
Da
Ck Qa
Ck Qb
Ck Qa
c
b
outputs
a
4
5
6
7
8
Shift registers
Classification, basic function, uses:
• Plain shift registers:
– Serial-in serial-out – SISO (also first-in first-out
– FIFO)
– Serial-in parallel-out – SIPO
– Parallel-in serial out – PISO
– Parallel-in parallel-out – PIPO
• Counters based on shift registers
– Ring counter
– Johnson counter
• Shift register and feedback based circuits
9
Shift registers
•
•
•
•
Serial-in serial-out – SISO
Serial-in parallel-out – SIPO
Parallel-in serial out – PISO
Parallel-in parallel-out – PIPO
10
11
Plain shift registers
CLOCK
SERIN
SEROUT
12
13