RS-422, also known as Recommended Standard 422, is a serial communication standard developed by the Electronic Industries Association (EIA) in the United States. It is commonly used for balanced data transmission over long distances and provides differential signaling, making it less susceptible to noise and interference compared to single-ended signaling.
RS-422 uses a differential signaling scheme, where each signal is represented by a pair of wires: a positive (non-inverting) wire and a negative (inverting) wire. This allows for greater noise immunity and enables longer transmission distances. The specification defines multiple signal lines for different purposes, including data transmission, control signals, and ground reference. Here is an overview of the commonly used signal lines in an RS-422 interface:
Transmit Data + (TX+): This wire carries the positive (non-inverting) signal for transmitting data from the sender.
Transmit Data - (TX-): This wire carries the negative (inverting) signal for transmitting data from the sender.
Receive Data + (RX+): This wire carries the positive (non-inverting) signal for receiving data at the receiver.
Receive Data - (RX-): This wire carries the negative (inverting) signal for receiving data at the receiver.
Request to Send (RTS+): This wire is used for hardware flow control, allowing the sender to request permission to transmit data.
Request to Send (RTS-): This wire is the negative (inverting) counterpart of RTS+, completing the hardware flow control.
Clear to Send (CTS+): This wire is used for hardware flow control, indicating that the receiver is ready to accept data.
Clear to Send (CTS-): This wire is the negative (inverting) counterpart of CTS+, completing the hardware flow control.
Data Terminal Ready (DTR+): This wire is used for signaling that the sender is ready to transmit data.
Data Terminal Ready (DTR-): This wire is the negative (inverting) counterpart of DTR+, completing the signaling.
Data Set Ready (DSR+): This wire is used for signaling that the receiver is ready to receive data.
Data Set Ready (DSR-): This wire is the negative (inverting) counterpart of DSR+, completing the signaling.
Signal Ground (SG): This wire serves as the common reference ground for all signals in the RS-422 interface.
It is important to note that the number of wires in an RS-422 interface can vary depending on the specific implementation and the requirements of the system. The above list includes the most commonly used signal lines, but additional wires may be present for power supply, shielding, or other purposes as per the system design.
In summary, an RS-422 interface typically consists of at least four pairs of wires for differential signaling (TX+, TX-, RX+, RX-), along with additional wires for hardware flow control (RTS+, RTS-, CTS+, CTS-), signaling (DTR+, DTR-, DSR+, DSR-), and a signal ground (SG). The total number of wires in an RS-422 interface will depend on the specific implementation and any additional requirements of the system.
