Ports
RS-485 Configuration
8-16
A large number and varieties of protocols run over RS-485. However, the SCS does not convert or
interpret serial data. It only moves data between serial and Ethernet. Any RS-485 protocol will have
to be implemented by host software.
Note:
See your Installation Guide for the RS-485 pinouts.
To enable RS-485 mode on the SCS, enter the
Define Protocols RS485
command. RS-232 mode is enabled
by default.
Figure 8-40:
Enabling RS-485 Mode
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 8-41:
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 8-42:
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 ENABLED
Local>> DEFINE PROTOCOLS RS485 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
(SCS)
Summary of Contents for SCS
Page 14: ...xii ...
Page 171: ...Modem Sharing Examples 10 6 ...
Page 314: ...Command Reference Service Commands 12 110 ...
Page 403: ...Show 802 11 Errors Rightmost Number B 5 00000002 Internal error 00000001 Internal error ...
Page 424: ...Index 13 ...