characteristic
1. Few signal cables
The RS-232 bus defines 25 lines, consisting of two signal channels, namely the first channel (called the main channel) and the second channel (called the secondary channel). The RS-232 bus can realize full-duplex communication, usually using the main channel, and the secondary channel is used less. In general applications, the use of 3 ~ 9 signal lines can achieve full duplex communication, the use of three signal lines (receiving line, sending line and signal ground) can achieve a simple full duplex communication process.
2. Flexible baud rate selection
RS-232 provides standard transmission rates of 50b\/s, 75b\/s, 110b\/s, 150b\/s, 300b\/s, 600b\/s, 1200b\/s, 2400b\/s, 4800b\/s, 9600b\/s, 19200b\/s, which can be flexibly adapted to different rates of equipment. For slow peripherals, a lower transfer rate can be selected; conversely, a higher transfer rate can be selected. [1]
3. Use negative logic for transmission
The level of logic \"1\" is defined as -5V to -15V, and the level of logic \"0\" is defined as 5V to 15 V. The purpose of selecting this electrical standard is to improve the anti-interference ability and increase the communication distance. RS-232 has a noise tolerance of 2V, and the receiver will be able to recognize signals up to 3V as logical \"0\" and signals down to -3 V as logical \"1\".
4. The transmission distance is long
Because RS-232 adopts serial transmission mode and converts TTL level of microcomputer to RS-232C level, its transmission distance can generally reach 30 m. If the current ring with photoelectric isolation of 20 mA is used for transmission, the transmission distance can reach 1000 m. In addition, if the RS-232 bus interface is coupled with a Modem, it can be transmitted through wired, wireless or optical fiber, and the transmission distance can be further.
5. Two physical interfaces
One connector of the RS-232 interface is the 25-pin plug holder of the D13-25, usually the plug is at the DCE end and the socket is at the DTE end.