Lantronix MSS4-D, Installation Manual

Page: 37 / 95

Configuration RS-485 Configuration
4- 7
4.3.1 Two-wire Mode
In two-wire mode, the MSS 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 4-9: Example Two-wire Mode Network
In a two-wire RS-485 network, the MSS 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 4-10: Enabling Two-Wire RS-485 Mode
Note:
For two-wire mode, the TXDrive setting must be set to Automatic (see
TXDrive on page 4-8). If you enable two-wire mode and TXDrive is set
for Always, the MSS will return an error.
Local>> CHANGE RS485 PORT 3 MODE 2WIRE
TX-
TX+
TX
RX
Shield
-
-
+
+
-
+
+
-
RX
TX
Shield
Shield
Shield
-
+
-
+
TX
RX
Sh
Sh
-
+
-
+
TX
RX
Sh
Sh
-
+
-
+
TX
RX
Sh
Sh
¥
¥
¥
Shield
Slave Slave Slave
Slave
Master
(MSS)