Key Facts for Lab 18

Chapter 16: Sequential Logic Continued

Ripple Counters

If we connect a series of flip-flops together then we can construct circuits that can count in binary., A circuit built with n flip-flops can count from 0 to 2ⁿ-1. With 2 flip-flops we can build a 2-bit counter.

This counts through the states 0, 1, 2, and 3 and is often called a divide-by-4 since its O1 output is at 1/4 the frequency of its clock input.

By adding extra logic we can cut the count short at any lower number using the reset inputs of the flip-flops. For example here is a simple divide-by-ten.

The NAND gate generates a reset pulse when the output reaches %1010 (decimal 10) and then the counter starts over from zero.