Counting is a simple and basic operation. The counter is the logic circuit that realizes this operation. In the digital system, the counter mainly counts the number of pulses to realize the functions of measurement, counting and control. It also has the function of frequency division. The counter is composed of a basic counting unit and some control gates. The counting unit is composed of a series of various triggers with the function of storing information. These triggers include RS triggers, T triggers, D triggers and JK triggers.器等。 Counters are widely used in digital systems. For example, in the controller of an electronic computer, the instruction address is counted so that the next instruction can be taken out in sequence. The number of additions and subtractions is recorded when the arithmetic unit performs multiplication and division operations. The counting of pulses in the instrument, etc. The counter can be used to display the working status of the product. Generally speaking, it is mainly used to indicate how many copies of the folding and collating work the product has completed. Its main indicator lies in the number of digits of the counter, the common ones are 3 digits and 4 digits. Obviously, a 3-digit counter can display up to 999, and a 4-digit counter can display up to 9999.