Emerson FB1100 Instruction Manual page 45

When connecting COM2 or COM3 to an RS-485 port on another device (for example, a
transmitter), use a cable with configurations as shown in
Figure 2-30: Connecting a Device to COM2 or COM3 Using RS-485

COM2 does not have its own GND terminal. Use either GND terminal on the COM1 terminal
block.

COM3 does not have its own GND terminal. Use either GND terminal on the COM1 terminal
block.
Regardless of the interface standard (RS-232 or RS-485), you must use FBxConnect to configure
the port for proper usage.
Installation
Emerson FB1100 Flow Computer Instruction Manual
Figure 2-30:
D301752X012
July 2017
RS-485 Port
(COM2) on
FB device
RS-485 Port
on external device
RS-485 Port
on external device
RS-485 Port
(COM3) on
FB device
39