After the computer is started normally, the address of the RS232 port COM1, COM2, COM3, and COM4 is generally arranged in 3F8, 2F8, 3E8, 2E8, and the register address for understanding the external state is set to 3FE, 2FE, 3ee, 2ee, with 3FC, 2FC, 3EC, 2EC, respective The pin arrangement of the RS232 interface is as follows:
D-type 25-core connector D-type 9-core joint PIN8 .... CD Pin1 PIN3 ... RXD PIN2 PIN2 ... TXD PIN3 PIN20 PIN6 ... DSR PIN6 PIN4 .. .Rts pin7 PIN5 ... CTS PIN8 PIN22 ... RI PIN9 Signal Name TXD Transmit Data RXD Receive Data RTS Request To Send CTS CLEAR TO Send DSR Data Set Ready DTR DATA TERMINAL READY SGNAL GROUND RI RING INDICATOR CD Carrier Detect
Pin 1CD (Carrier Detect) carrier detection, modem notification PCPC-> MODEMPIN2RXD (Receive) Receive Characters, receive information MODEM-> PCPIN3TXD (Transmit) Transfer Character PC-> MODEMPIN4DTR (DataTerminal Ready) Data is ready, tell ModeMPC-> MODEMPIN5GND (GROUND) Ground PC = Modempin6DSR (Data Set Ready) Data Ready, telling PCMODEM-> PCPIN7RTS (Request to send) Requirements to transfer, PC requires modempc-> modempin8CTS (Clear to send) clear transmission, modem notification PCMODEM -> PCPIN9RI (Ring Indicator) ring detection, modem notification PCMODEM-> PC
