74LS161 is a commonly used four-bit binary preset synchronous addition counter. It can be flexibly used in various digital circuits and microcontroller systems to achieve many important functions such as frequency dividers. 74LS161 also has a carry output CO, whose logical relationship is CO=Q0•Q1•Q2•Q3•CET. Reasonable application of counter clear function and set number function, a piece of 74LS161 can form any hexadecimal frequency divider below hexadecimal.