Page 199 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes shift), this has the effect of multiplying the number by two. With suitable gating arrangement a
serial shift register can perform both operations.
A bidirectional, or reversible, shift register is one in which the data can be shift either left or right.
A four-bit bidirectional shift register using D flip-flops is shown in Figure 11.16.

Figure 11.16: Four-Bit Bidirectional Shift Register Using D Flip-Flops

Here a set of NAND gates are configured as OR gates to select data inputs from the right or left
adjacent bistables, as selected by the LEFT/RIGHT control line.
Figure 11.17: The LEFT/RIGHT Control Line

4-Bit Bidirectional Universal Shift Registers (74HC194)
The 74HC194 is a universal bi-directional shift register. It has both serial and parallel input and
output capability.
Figure 11.18: The 74HC194 4-Bit Bidirectional Universal Shift Register

D 0 D 1 D 2 D 3

(3) (4) (5) (6)
(1)
CLR SRG 4
S 0 (9)
(10)
S
1
(2)
SR SER
(7)
SR SER
(11)
CLK C
(15) (14) (13) (12)
Q 0 Q 1 Q 2 Q 3

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