SHIFT REGISTERS&

APPLICATIONS

Registers:

We can say that A register is an extension of a flip-flop that can store multiple bits.

Registers are commonly used as temporary storage in a processor.They are faster and more convenient than main memory.

More registers can help speed up complex calculations.

This registers are of two types1. Serial load2. Parallel load

3. Serial load registers:

Serial in serial out Serial in parallel out

2. Parallel load register:

Parallel in serial out Parallel in parallel out

Serial in serial out:After each clock pulse data will enter into

the flip flop serially and the output of the present flip flop is fed to the next after the 2nd clock pulse and so on..

Serial in parallel out:Same as in SISO after 4 clock pulses

data is loaded into the register and the data will be available at the output after 4 clock pulses where as in SISO the will be available at the out put after 8 clock pulses.

Parallel in serial out:It shows the PISO register where the

mode control is used. When mode is low the data is clocked into the flip flop and the data is shifted when the mode bit is high

Parallel in parallel out:In PIPO registers the data will appear

immediately at the output after a single clock pulse and there is no clock delay.This PIPO register are also known as general register because of no shifting operation.

APPLICATIONS

Pseudo random pattern generator

Ring counter

Johnson counter or twisted counter

Ring counter:

Ring counter is a shift register in which the output of the last flip flop is fed to the input again.

For every clock pulse the data shifted into the next flip flop thus it can count only N states.

Ring counter

Johnson counter

The complement of the output of the last stage is connected back to the D input of the first stage.

Also called the twisted-ring counter.

Require fewer flip-flops than ring counters but more flip-flops than binary counters.

An n-bit Johnson counter cycles through 2n states.

Require more decoding circuitry than ring counter but less than binary counters.

Johnson counter

Pseudo random pattern generator

It is a simple shift register where the vacated bit of is filled with the exclusive-or of last two bits in the shift register.

By using this for a n bit shift register we can generate 2^n patterns.

This is very useful in test pattern generation.

Pseudo random pattern generator

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