Serial communication is a communication method that uses one or two transmission lines to send and receive data, and that data is continuously sent and received one bit at a time.Since it allows for connections with few signal wires, one of its merits is its ability to hold down on wiring material and relaying equipment costs.
RS-232C/RS-422A/RS-485 are EIA (Electronic Industries Association) communication standards.Of these communication standards, RS-232C has been widely adopted in a variety of applications, and it is even standard equipment on computers and is often used to connect modems and mice.Sensors and actuators also contain these interfaces, many of which can be controlled via serial communication.
This serial communication standard is widely used and is often equipped on computers as standard.It is also called "EIA-232".The purpose and timing of the signal lines and the connectors have been defined (D-sub 25-pin or D-sub 9-pin).Currently the standard has been revised with the addition of signal lines and is formally called "ANSI/EIA-232-E".However, even now it is generally referred to as "RS-232C".
This standard fixes problems in RS-232C such as a short transmission distance and a slow transmission speed.It is also called "EIA-422A".The purpose and timing of the signal lines are defined, but the connectors are not.Many compatible products primarily adopt D-sub 25-pin and D-sub 9-pin connectors.
This standard fixes the problem of few connected devices in RS-422A.It is also called "EIA-485".RS-485 is forward compatible standard with RS-422A.The purpose and timing of the signal lines are defined, but the connectors are not.Many compatible products primarily adopt D-sub 25-pin and D-sub 9-pin connectors.
In RS-232C, the connectors to use and the signal assignments have been defined and are standardized.The figure to the right describes the D-sub 9-pin signal assignments and signal lines.
In RS-232C, the connectors and signal assignments have been standardized, so many standard-compliant cables are available commercially.However, equipment comes in the following types, and depending on the equipment that will be connected, a straight cable or a crossover cable is required.
Data communication equipment.This term indicates equipment that passively operates such as modems, printers, and plotters.
Data terminal equipment.This term indicates equipment that actively operates such as computers.
In serial communication, data is sent one bit at a time using one signal line, so in order for the receiving side to accurately receive the data, the sending side must know at what speed it is sending each bit.In RS-232C, synchronous communication and asynchronous communication standards have been defined.For peripheral equipment used for measurements or control, the previously mentioned full-duplex communication and asynchronous communication are typically used.