The counter is a type of serial data transfer device which is used for different types of counting. In a Counter, Count may hold after a limit of time again and again or no limit of time (no specific gap time between each counting steps).

## Counter

The counter can follow different types of sequences. But the most simple sequence is the binary sequence.

### Use of counter

• Counting events
• Digital electronics operation control
• Timing signaling
• Digital watches
• Digital computers
• Converting parallel data into signal data

### Types of counter

Respecting the input clock pulse counter has two types-
1. Asynchronous counter
2. Synchronous counter

### Asynchronous

In these counters output of one Flip-Flop is used as the clock pulse of the other Flip-Flop. Example: Ripple counter

The asynchronous ripple counter can be divided into two types. They are:

#### Ripple up

Ripple up counter Count the numbers from smaller to larger.

#### Ripple down

Ripple down counter counts the numbers larger to smaller.

### Synchronous

Here a single clock pulse changes the states of all the Flip-Flops used on the counter. Example: Ring counter, Mod-10 counter.

### Binary Counter

The counter which follows the binary sequence is called a binary counter. A counter can count limited numbers. So, an n - bit binary counter can sequentially count 0 to 2n-1 numbers. And this is built by using n number of Flip-Flops.

Here we can see a transition state diagram of a 3 bit binary counter. After counting binary sequence 111 next step it returns to 000 states.

Another type of counter is the BCD counter. In the case of the BCD counter, the highest state is 10. It counts 000 to 1001.

How many numbers a counter can count is called the modulus of that counter. If a counter is built by n number of Flip-Flops then its modulus = 2ⁿ.

### Ripple counter

It is the easiest and a simple counter. It is an Asynchronous counter that means the output of each Flip-Flop helps to trigger its next Flip-Flop.

In another way we can say, the trigger is done by Clock Pulse of all Flip-Flop(Escaping the first one) changing the output condition of others.

n bit ripple counter is built with n number of Flip-Flops. here the Flip-Flops stays in row-wise and the output of one Flip-Flop work as a clock pulse of another Flip-Flop.

In this picture, there is a 3-bit binary ripple counter using a T-Flip Flop. We know if we give 1 in clock pulse for T-Flip Flop then it toggles always. That means Here all Flip-Flop input has given '1'.

If we give a clock pulse in Flip-Flop 0 then it will toggle. That means each time it will make '0' to '1' and '1' to '0'. This output will work as a clock pulse of Flip-Flop 1. That means when Q₀ =1 only that time it will toggle. So, Flip-Flop 1 will toggle 2 times.

This output of Flip-Flop 1 Q will work as a clock pulse of Flip-Flop 2.

So that, Q=1 will be here also two times. That's why Flip-Flop 2 will toggle 4 times.