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MSS User Guide 4: Configuration
4-10
TXDrive
The MSS-VIA can be configured to always drive the TX (transmit) signal, or tri-state
(transmit, receive, or ignore) when not actively transmitting. The Change RS485 TXDrive
command takes one of two parameters. The Always parameter sets the MSS for
continuous TXDrive, both high and low. The Automatic parameter sets the MSS for
TXDrive only when transmitting.
Figure 4-27: Changing TXDrive for MSS4
Local>> CHANGE RS485 PORT 2 TXDRIVE AUTOMATIC
Figure 4-28: Changing TXDrive for MSS-VIA
Local>> CHANGE RS485 TXDRIVE AUTOMATIC
Note: You can only set TXDrive for Always when using four-wire mode. It must be set to
Automatic for two-wire mode.
Termination
RS-485 connections must be terminated properly in order to work. Termination is
necessary when using long cable runs, although only end nodes should be terminated.
Figure 4-29: Enabling RS-485 Termination for MSS4
Local> CHANGE RS485 PORT 2 TERMINATION ENABLED
Figure 4-30: Enabling RS-485 Termination for MSS-VIA
Local> CHANGE RS485 TERMINATION ENABLED
Slave devices should be set for automatic termination using the Change 485
Termination TX Auto command.
A Note About RS-422 Networking
The MSS is compatible with RS-422 networks in four-wire RS-485 mode. Connect the
MSS to a single slave device using a swapped cable, as shown below, and configure the
MSS as if you were going to use it for four-wire RS-485 networking.