Configuration
Serial Port Configuration
4-7
It is important to connect the transmitter of the master device to the wire that is connected to the receive
terminals on the slave devices, and connect the receiver of the master device to the wire that is connected
to the transmit terminals on the slave devices. In essence, the master device will be connected to the slave
devices with a swapped cable.
Figure 4-12:
Enabling Four-Wire RS-485 Mode
TXDrive
The MSS can be configured to either always drive the TX (transmit) signal or to let the attached device
control the TX signal (tristate) when not actively transmitting. The Change RS485 Port [Portlist] TXDrive
command takes one of two parameters. The Always parameter sets the MSS for continuous TXDrive, so
TX will never be tristated. The Auto parameter sets the MSS for TXDrive when transmitting and tristate
while idle.
Figure 4-13:
Changing TXDrive
Note:
You can only set TXDrive for Always when using four-wire mode. The Always parameter
has no effect 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. The termination option is disabled by
default.
Figure 4-14:
Enabling RS-485 Termination
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.
Figure 4-15:
RS-422 Connection
Serial Port Configuration
The serial ports are set at the factory for 9600 baud, 8 data bits, one stop bit, and no parity. Remember that
ports should be logged out after configuration so the changes will go into effect.
On the MSS4, the first serial port is designated as the console port. However, this is not a dedicated console
port and is fully configurable.
Local>> CHANGE RS485 PORT 3 MODE 4WIRE
Local>> CHANGE RS485 PORT 3 TXDRIVE AUTO
Local>> CHANGE RS485 PORT 3 TERMINATION ENABLED
TX
RX
RX
TX
TX-
TX+
RX+
RX-
Shield
Shield
RX-
RX+
TX+
TX-
Shield
Shield
Master
(MSS)
Slave
