此原理图为医用呼叫系统主机部分，系统采用PIC16F877A作为主控芯片，能够带动50门分机工作，已调试成功，硬件电路完全成熟-This picture shows the principle of the host part of the medical call system, the system uses PIC16F877A as the main chip can drive 50 extension work, has been debugged, hardware fully mature