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RS-232 (also known as EIA RS-232) is one of the commonly used serial communication interface standards. It was jointly formulated in 1970 by the Electronic Industries Association (EIA) in conjunction with Bell Systems, modem manufacturers and computer terminal manufacturers.
It has the characteristics of less signal lines, flexible baud rate selection, negative logic transmission and long transmission distance.
In serial communication, both sides of the communication are required to adopt a standard interface, so that different devices can be easily connected for communication.
RS-232-C interface, also known as EIARS-232-C, is the most commonly used serial communication interface.
It is a standard for serial communication jointly formulated by the Electronic Industries Association (EIA) of the United States in 1970 in conjunction with Bell Systems, modem manufacturers and computer terminal manufacturers.
Its full name is "Serial Binary Data Exchange Interface Technology Standard between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)", which stipulates the use of a 25-pin DB-25 connector, and each The signal content of each pin is specified, and the level of various signals is also specified.
Later, IBM's PC simplified RS232 into a DB-9 connector, which became the de facto standard. The RS-232 port of industrial control generally only uses three lines of RXD, TXD and GND.
1. Serial port protocol standard
The full name of the RS-232C standard (protocol) is the EIA-RS-232C standard, where EIA (Electronic Industry Association) stands for the American Electronics Industry Association, RS (recommended standard) stands for the recommended standard, 232 is the identification number, and C stands for the latest RS232. Modified (1969), before that, there were RS232B, RS232A.
It specifies connecting cables and mechanical, electrical characteristics, signal functions and transmission processes.
Common physical standards include EIARS-422A, EIA RS-423A, and EIARS-485.
Only EIA RS-232C (referred to as 232, RS232) is introduced here.
For example, the COM1 and COM2 interfaces currently on IBM PC are RS-232C interfaces.