Use CD4511/CD4518 to complete two-digit decimal counting, one of the decimal counters is connected as: IEN terminal is used as the counting enable terminal (high level is valid), 1CP is used as the counting clock input terminal (the rising edge trigger is valid), and the single digit is counted; A decimal counter is connected as: 2CP terminal is used as a counting enable terminal (active low), 2EN is used as a counting clock input terminal (falling edge trigger is valid, and 1Q3 of a + binary counter is used as a carry pulse, asynchronous technology connection mode), Count the decimal number. The 8421BCD code output by the two-digit counter is directly input to the respective decoding chip CD4511 for processing.