Specifications

Appendix C - Glossary of Terms RS-422 And RS-485 Applications Ebook
Page 120 of 137 Manual Documentation Number: <DocNumber>
www.bb-elec.com/
www.bb-europe.com/
Two-wire RS-485 at the other end. If using for two-wire RS-485, the devices
must be suitable for half duplex operation.
RS-422
A standard used to extend serial communications up to 4000 ft. between two
devices. Each channel of communications is converted to a differential signal
and carried on a twisted wire pair so that when the differential signal is
received, common mode noise is rejected. RS-422 generally has at least two
channels, receive and transmit. These are carried on four wires, and a signal
common/ground provides a reference for the receiver and transmitter. RS-422
can also handle handshaking signals using additional twisted pairs.
RS-422 Connector
This is the connector type used on the RS-422 side of a converter or device.
The EIA-422 standard does not specify a connector to be used with RS-422. In
actual products a variety of connectors are used.
RS-422 Port
A serial port which provides RS-422 differential inputs for receive and outputs
for transmit. Typical RS-422 ports support two channels.
RS-422 Transmit Enable
Some RS-422 devices can have the transmit driver enabled and disabled as is
done for RS-485. Disabling the transmitter when not used saves power on port
powered devices. It also allows a RS-422 device to operate as in a four -wire
"half 485" mode, the same as a four-wire RS-485 device.
Normal RS-422 devices have the transmitter enabled all the time. Controlled
transmitters are activated by setting the RTS line in the RS-232 device or the
RTS control in the UART. When the RTS line is not asserted, the transmitter is
set Off to a high impedance state.
RS-485
RS-485 is a multi-drop extension to the RS-422 standard. It uses differential
signals on twisted pairs for receive and transmit.