PURPOSE: To obtain a counter circuit which can be used for both the 12- and 24- hour systems by adding the gate to detect that the contents of the 10-hour digit counter of the counter circuit is 1 or 3 and the contents of the 1-hour digit counter is 2 respectively in the 24-hour system.

CONSTITUTION: 1-hour digit counter 1 is clocked by carry signal A of the minute counter. And when the contents of counter 1 becomes 10, the carry signal is supplied to 10-hour digit counter 2. At the same time, counter 1 is reset. In the case of the 12-hour system, signal H12 becomes 1. When counter 2 is 1 or 3 and counter 1 becomes 2, the carry signal is supplied to counter 2 with counter 1 reset. Thus, the fact that couner 1 is 0 and counter 2 is 0 or 2 is detected to have output as 12. While in the case of the 24-hour system, counter 1 and 2 are reset when counter 2 is 2 and counter 1 is 4 respectively.