利用串口来发送数字量信号只要连接串口的4号口和5号口就行，其中5号口为负，电压12V-Using the serial port to send digital signals as long as the connection port and 4 serial ports on the line 5, in which 5 mouth is negative, voltage 12V

MAX232芯片是美信公司专门为电脑的RS-232标准串口设计的接口电路,使用+5v单电源供电。-The MAX220–MAX249 family of line drivers/receivers is intended for all EIA/TIA-232E and V.28/V.24 communications interfaces, particularly applications where ±12V is not available.