Chapter 8: rs-422/485 connections/operation, Rs-422/485, Ignal – B&B Electronics 3PCIOU4 - Manual User Manual
Page 37: Esignations and, Db-9, Inout, Rs-422/485 signal designations
RS-422/ 485 Connections/Operation
Document Number 3PCI-0712m
Chapter 8
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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.