基于89c51的单片机的实验电路板的制作，开发了一块有较多功能但使用单面板的单片机实验板，适于业余爱好者自制。这个是第二部分。-89c51 microcontroller based on the experimental production of circuit boards, the development of a more functional but the single-chip single-sided board, suitable for amateur-made. This is the second part.