Different types of synchronous counters, ciruit diagram and working

There are 6 types of Synchronous counters:

Binary counters

Binary counters are most basic type of synchronous counters. Depending on the value of N, a synchronous counter counts from 0 to (2N - 1) and back to 0 again.

Up/down counters

A counter can be used to count in more than one direction. That is, you can use counter to count not only up but down too. The diagram shows below is of an up-down counter. Depending on how the user decides to count an event as up and other as down, the counter can be used to count the events based on his requirements. This is done by either making either the “up” or "down" inputs as high.

Loadable counters

Loadable counters can be used to count from a predefined count. That is, instead of counting from a 0, the counter will count from a initial count given by the user. This type of counter is called a loadable counter.

BCD counters

A BCD counter is a binary digit based counter which users 0 and 1 for counting. The counting is done in binary-coded decimal from 0000 to 1001 and back to 0000. As the counter resets after 1001, i.e. it starts from 0 and after a count of 9 it comes back to 0. Therefore, this counter does not have a straight binary count and has limited functionality.

Ring counters

In a ring counter, the registers are activated one by one in a circular manner. The flip-flops are set one by one; when a particular flip-flop is set, the others are cleared. A single high signal is circulated from one flip-flop to another to produce to produce the sequence of timing signals.

Johnson counters

The Johnson counter is a hybrid form of ring counter. It is also called the twisted ring counter. In this counter the inverse of the most significant bit output at the flip-flop is passed on to lest significant but at the flip-flop. The working can be understood by the truth table shown below. The sequence starts with all the bits of the counter being 0. At the next pulse, the 0 at the final counter will cause the 1’s to be shifted into register from left hand side. Similarly, when the 1’s reach the most significant flip-flop, 0’s will be inserted in the left most registers. This cross coupling between the between the inputs and the outputs of the registers is the base of working of the Johnson counter.