Omron Programmable Terminals NT31 NT31C - Manual (Page 140)

5-2 Section Connecting to the Host’s RS-422A/485 Port
129
Pin Nos. 9 and 10 Function
Shorted
Terminal resistance is applied.
Short only at the NT31/NT31C connected to the end of an
RS-422A/485 cable.
Open
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.
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.
Reference: S The internal circuit of the NT31/NT31C is shown below.
16 (RDA)
9 (TRM)
10 (RDB) +
−
Terminal resistor (120 Ω)
Making a connection here inserts a terminator between
+ (RDB) and
− (RDA).
S For details on setting the terminal resistance of the host unit, refer to setting
methods for each type of the communication.