The HCF4521B have a chain of 24 flip-flops with an input circuit that allows three modes of operation. The input circuit functions as a crystal or an RC oscillator or as an input buffer for an external oscillator. Each flip-flop performs a divide-by-two function giving a total count of 224 = 16,777,216. The count advances on the negative going edge of the clock. Access is available to the final seven stages giving the device added flexibility.