可预置可逆4位计数器，本文详细阐述其原理并附有电路原理图，程序用C/汇编语言分别编写，可随意供大家选择，对学单片机的掌握基础应用很有帮助！-Reversible 4-bit counter can be preset, the paper described the principles together with the circuit diagram, program using C/assembly language were written, are free for your choi