Question

A bidirectional 4-bit shift register is storing the nibble 1101. Its input is HIGH. The nibble 1011 is waiting to be entered on the serial data-input line. After three clock pulses, the shift register is storing ________

(a) 1101

(b) 0111

(c) 0001

(d) 1110

I had been asked this question by my college professor while I was bunking the class.

My question is taken from Universal Shift Registers topic in section Registers of Digital Circuits

Answer 1

Correct option is (b) 0111

Easiest explanation: Mode is high means it’s a right shift register. Then after 3 clock pulses enter bits are 011 and remained bit in register is 1. Therefore, 0111 is the required solution.

1011 | 1101

101 | 1110  -> 1^st clock pulse

10 | 1111  -> 2^nd  clock pulse

1 | 0111  -> 3^rd clock pulse.