Page 190 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Unit 11: Registers and Counters

• Two basic functions: data storage (Figure 11.2) and data movement (Figure 11.1) Notes
Shift Register:
• A register that allows each of the flip-flops to pass the stored information to its adjacent
neighbour

• Figure 11.1 shows the basic data movement in shift registers
Counter:
• A register that goes through a predetermined sequence of states
Figure 11.1: Basic Data Movement in Shift Registers

Datain

Datain Data out Data out Datain Data out
() Serial-in/shift right/ serial-out () Serial-in/shift left serial-out () Parallel-in/serial-out
a
b
c
Serial
Datain
Datain

Data out Data out
e
f
() Serial-in/parallel-out () Parallel-in/parallel-out () Rotate right () Rotate left
d
g
Storage Capacity:
The storage capacity of a register is the total number of bits (1 or 0) of digital data it can retain.
Each stage (flip-flop) in a shift register represents one bit of storage capacity. Therefore, the number
of stages in a register determines its storage capacity.
Figure 11.2: The Flip-Flop as a Storage Element

11.1.1 Serial-In/Serial-Out Shift Registers
The serial-in/serial-out shift register accepts data serially that is, one bit at a time on a single line.
It produces the stored information on its output also in serial form.
Basic four-bit shift register
Figure 11.3: Four D Flip-Flops

LOVELY PROFESSIONAL UNIVERSITY 185