Product manual

PX Range Product Manual Version 2.0 © Copyright Brainboxes Limited 2010 Page 21 of 37
outwards, and the fourth pair brings the CTS handshaking signal inwards. There is no need to carry
the ground from one device to another.
• Half Duplex Autogating Mode
The RS485 standard is similar to the RS422 standard upon which it is based. The main difference is
that up to 32 transmitter / receiver pairs may be present on the line at one time.
Although the card uses a 9 pin D connector, generally not all the lines are used for RS485 systems.
The RTS+/- and CTS+/- lines, though driven by the card, are usually not connected. In two wire Half-
Duplex configuration, the TXD+ line is connected to RXD+, whilst the TXD- line is connected to
RXD-. Only one pair of twisted wire cable is used in RS485 Half Duplex communication.
These are the two main wiring schemes:
o RS485 One Talker Many Listeners (Half Duplex)
o RS485 Many Talkers Many Listeners (Half Duplex)
Please see Section 8.2: Device Pinout for wiring diagrams.