MCP3421 12bit~18bit 的 ADC 用于微小电压采集 proteus 8 仿真 C51程序 Keil4/5编程 串口打印电压值 （可虚拟串口仿真）(MCP3421 12bit~18bit ADC for small voltage acquisition Proteus 8 simulation C51 program Keil4/5 programming serial port printing voltage value (virtual serial por