232转485电路，电路从串口取电，无需外接电源-232 to 485 circuits, the circuit to take power from the serial port, no external power supply

1.异步通信软件模拟2.基于RS-232的串口通信3.基于RS-485的多机通信4. I2C总线协议的软件实现5. SPI总线在单片机系统中的实现6.-wire-1. Asynchronous communication software simulation 2. Based on the RS-232 serial communication 3. Based on the RS-485 Multi-machine communication 4. I2C bus protocol soft