0195136047.pdf

298 DIGITAL BUILDING BLOCKS AND COMPUTER SYSTEMS

n 0

n 1

n 2

I 7

I 0

I 7 I 6 I 5 I 4 I 3 I 2 I 1 I 0

I 1

I 2

I 3

I 4

I 5

I 6

I 7

I 6

00

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01

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I 5

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1

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I 4 I 3

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I 2

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Outputs

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I 1 I 0

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n 2

(a) (b)

(c)

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11

11

n 0

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Inputs

n 1

n 0

Figure 6.2.28-to-3 encoder.(a)Block diagram.(b)Truth table.(c)Logic diagram.

convenient way that is needed for the operations involved. Right-shifting registers are employed

in multiplication algorithms, whereas left-shifting registers are utilized in division algorithms.

Registers that are capable of shifting the data to the left or right are known asbidirectional

shift registers. The register along with additional gates on a single chip forms an IC component

known as theuniversal register,which usually includes the shift-left, shift-right, parallel-input,

and no-change operations.

Counters

The shift register can be used as a counter because the data are shifted for each clock pulse. A

counter is a register that goes through a predetermined sequence of states when input pulses are

received. Besides, computers, timers, frequency meters, and various other digital devices contain

counters for counting events.

There are what are known asripple(asynchronous),synchronous,andringcounters. In

ripple counters, the output of each flip-flop activates the next flip-flop throughout the entire

sequence of the counter’s states. In a synchronous counter, on the other hand, all flip-flops

are activated (triggered) simultaneously through a master clock connected to the clock inputs

of all flip-flops. In a ring counter, as in a synchronous counter, all flip-flops are triggered