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RS-422/ 485 Connections/Operation

Document Number 3PCI-4310m Chapter 8 31

RS-422/485 Mode

In RS-422/RS-485 mode MIport serial ports provide two sets of differential signal pairs

and signal ground for each port. The RS-422 and RS-485 standards use balanced

differential drivers and receivers for each signal. This facilitates greater communication

distances than unbalanced systems such as RS-232.

RS-422 operation is suitable for interconnecting a computer and one device for full

duplex (point-to-point) bi-directional communication, or a computer and several devices

for unidirectional (point-to-multipoint) communication. RS-422 interfaces are commonly

used for video editing/control, camera control, electronic signage, television

studio/satellite dish control, performance lighting and audio equipment control.

RS-485 operates with the same signals and signal levels as RS-422 but differs in that it

allows multiple devices to share the same communication link using half duplex (2-wire)

or full duplex (4-wire) connections. RS-485 interfaces are commonly used in

manufacturing and industrial/commercial control applications such as programmable

logic controllers, telemetry, and process control.

RS-422/485 Signal Designations and DB-9 Pinout

Name Description Direction DB-9 M Pin

RDA(-) Receive Data A (-) Input 1

TDB(+) Transmit Data B (+) Output 2

TDA(-) Transmit Data A (-) Output 3

GND Signal Ground ------ 5

RDB(+) Receive Data B (+) Input 9

Figure 14. RS-422/485 Signal Designations and DB-9 Pinout

Note: Refer to Appendix B for additional cable configurations and

pinouts

RS-422/485 Signal Designations

Typically RS-422 and RS-485 interfaces use five lines including two signal pairs and

ground. One signal pair is the transmit pair, labeled TDA(-) and TDB(+). The other

signal pair is the receive pair, labeled RDA(-) and RDB(+). Signal ground is labeled

GND.

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