Omron Programmable Terminals NT31 NT31C Setup Manual page 140

Connecting to the Host's RS-422A/485 Port
Reference:
Pin Nos. 9 and 10
Shorted
Open
Note Before connecting or disconnecting cables between devices, make sure that the
power supply to all of the connected devices (NT31/NT31C, PC, etc.) is OFF.
S The internal circuit of the NT31/NT31C is shown below.
+
−
Terminal resistor (120 Ω)
S For details on setting the terminal resistance of the host unit, refer to setting
methods for each type of the communication.
Function
Terminal resistance is applied.
Short only at the NT31/NT31C connected to the end of an
RS-422A/485 cable.
Terminal resistance is not applied.
Leave the terminals open when connecting an NT31/NT31C
anywhere other than at the end of the RS-422A/485 cable.
10 (RDB)
16 (RDA)
Making a connection here inserts a terminator between
+ (RDB) and − (RDA).
9 (TRM)
Section 5-2
129