User Manual

Ports RS-485 Configuration

8-16

8.10.1 Two-wire Mode

In two-wire mode, the SCS operates in half duplex: one pair of wires shares transmit and receive signals,

and an optional third wire can be used for shield/ground. The main advantage of using two-wire mode is

reduced cabling costs.

Figure 8-40: Example Two-wire Mode Network

In a two-wire RS-485 network, the SCS must turn its transmitter on when it is ready to send data and then

off for a certain period of time after the data has been sent so that the line is available to receive again. At

most baud rate settings, the timing delay is typically one character length with a maximum of 1.5 character

lengths.

Figure 8-41: Enabling Two-Wire RS-485 Mode

Note: For two-wire mode, the TXDrive setting must be set to Automatic (see TXDrive

on page 8-17). If you enable two-wire mode and TXDrive is set for Always, the

SCS returns an error.

Local>> DEFINE PROTOCOLS RS485 MODE 2WIRE

TX-

TX+

Shield

Slave Slave Slave

Slave

Master

(SCS)