Asynchronous Counters

When a group of flip-flops are connected together so that they store related information, they are known collectively as a register. Certain types of register can be used for the purpose of counting pulses, and are known as counters. An asychronous counter or serial counter is one in which the pulses are applied at one end of the counter, and the process of adding each pulse has to be completed before the ‘carry bit’ is propagated to the following stage. The following stage has then to add the carry bit to the number in that stage. That is, the carry bit appears to ‘ripple’ through the length of the counter until the count is complete. As a result, asynchronous counters are sometimes known as ripple-through counters.