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What Pins Are Needed for 2- and 4- Wire Transmission with RS-485 Serial Communication?

Hardware: Serial>>RS-485>>PCI-485/2

What pins are needed for 2- and 4- wire transmission with RS-485 serial communication?

For 2- wire and 4- wire transmission, TXD+, TXD-, RXD+, and RXD- are used.

In 4-wire transmission (full duplex), 4 wires run from TXD or RXD on the master to the opposite (TXD or RXD) on the slave(s).
TXD+ <=> RXD+
TXD- <=> RXD-
RXD+ <=> TXD+
RXD- <=> TXD-

In 2-wire transmission (half- duplex), TXD+ and RXD+ on the master are wired together to TXD+ and RXD+ on the slave(s). TXD- and RXD- on the master are wired together to TXD- and RXD- on the slave(s).

The pinout for a DB-9 is shown below.

Related Links:
KnowledgeBase 17M6L0TI: What Are the Different Transceiver Modes on the NI RS-485 Serial Cards?

Manual: Serial Quick Reference Guide

Developer Zone Example: How to Do Serial I/O and Change Transceiver Modes Programmatically using Visual C++


DB-9 Male.gif - DB-9 Male.gifRS-485 Topology 2-wire.gif - RS-485 Topology 2-wire.gif
RS-485 Topology 4-wire.gif - RS-485 Topology 4-wire.gif

Report Date: 09/27/2004
Last Updated: 11/17/2007
Document ID: 3DQBQ0OY

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