---
title: "Short note: Shift register and counter"
subject: "Basic Electronics Engineering"
chapter: 6
key: "semester_2/basic_electronics_engineering:short-note-shift-register-counter"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-shift-register-counter
site: BCT Engineering
---

# Short note: Shift register and counter

Basic Electronics Engineering · Chapter 6: Digital Electronics

- Asked in: 2067 Chaitra, 4 marks
- Video: [Counters and Shift Registers - Digital Electronics Tutorials](https://www.youtube.com/watch?v=vsp4r5xgbdc) — Instrumentation Tools
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/short-note-shift-register-counter
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-6

## Question

Write a short note on shift register and counter.

## Short answer

A shift register is a serial chain of flip-flops shifting data one bit per clock pulse; types include SISO, SIPO, PISO, PIPO. A counter is a sequential circuit that counts clock pulses through a fixed state sequence; asynchronous ripple counters are simple, synchronous counters are faster, used for frequency division and counting.

## Answer

#### Shift register

A **shift register** is a group of flip-flops connected in series, so that the stored binary data shifts by one position on every clock pulse. An n-bit register uses n flip-flops (D or JK) and stores n bits.

```text
 Serial   +----+   +----+   +----+   +----+
 in ----->| FF0|-->| FF1|-->| FF2|-->| FF3|--> Serial out
          +----+   +----+   +----+   +----+
             ^        ^        ^        ^
 CLK --------+--------+--------+--------+
```

Types: SISO (serial-in serial-out), SIPO, PISO, PIPO. Uses: temporary data storage, serial-to-parallel and parallel-to-serial conversion, time delay, and ring or Johnson counters.

#### Counter

A **counter** is a sequential circuit made of flip-flops that counts the clock pulses and goes through a fixed sequence of states.

- **Asynchronous (ripple) counter:** the output of one flip-flop is the clock of the next; simple but slow.
- **Synchronous counter:** all flip-flops receive the same clock; faster.
- An n-bit counter has a modulus up to 2ⁿ (a 3-bit counter counts 0 to 7). A BCD (decade) counter counts 0 to 9.
- Up, down, and up/down counters exist.

Uses: frequency division, digital clocks, event counting, timers, frequency meters.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. A shift register is:
   A. Flip-flops in series that shift stored data by one position on each clock pulse
   B. A combinational adder
   C. A single flip-flop
   D. A decoder
   Answer: A. The answer states this: Flip-flops in series that shift stored data by one position on each clock pulse. (Key point: Shift register)

2. Which is a shift register type?
   A. MUX
   B. PISO
   C. XOR
   D. ADC
   Answer: B. The answer states this: PISO. (Key point: Shift register types)

3. In an asynchronous (ripple) counter:
   A. All flip-flops get the same clock
   B. No flip-flops are used
   C. The output of one flip-flop is the clock of the next
   D. It is faster than synchronous
   Answer: C. The answer states this: The output of one flip-flop is the clock of the next. (Key point: Ripple counter)

4. A 3-bit counter counts:
   A. 0 to 3
   B. 0 to 9
   C. 1 to 8
   D. 0 to 7
   Answer: D. The answer states this: 0 to 7. (Key point: Counter modulus)

## Related in other subjects

- [Shift register uses; switched tail ring counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Aswitched-tail-ring-counter) — Digital Logic, chapter 7
- [Shift register uses; 4-bit ring counter](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Aring-counter-4bit) — Digital Logic, chapter 7
- [PISO shift register with 1011 data](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Apiso-1011-store-retrieve) — Digital Logic, chapter 7, asked 4×
- [4-bit PISO shift register working](https://www.bctengineer.com/question.md?key=semester_3%2Fdigital_logic%3Apiso-generic-circuit) — Digital Logic, chapter 7, asked 2×