RLE FMS V.1.13 - Manual (Page 136)

136 FMS User Guide 970.484.6510
4 Advanced Communications - Modbus, BACnet, and Telnet
4.2.2 EIA-485
The EIA-485 COM Port 1 on the FMS is used to connect the FMS-as a Modbus Master-to one
or more Modbus Slave devices or it is used to connect a Modbus Master device to the FMS as
a Modbus Slave. The Modbus EIA-485 is active over COM1 (TB5 Pins 8, 9 and 10). The EIA-
485 port allows communications between one Modbus Master and one or more Modbus Slave
devices. EIA-485 can accommodate up to 4,000 feet (1,219m) of cable length. There are many
variations on how terminals are labeled on EIA-485 2-wire (e.g., some devices use (+) and (-)
or A and B, and some use (-) and (+) or B and A. Therefore, if a Slave unit is not responding,
try swapping the wires.
Figure 4.3 EIA-485 Wiring Connections
Pin Description
8 EIA-485(+)
9 EIA-485(-)
10 Ground
Table 4.2 COM1 TB5 Pin Out