MODBUS RTU Instruction Manual - 2017-11-02.docx
Page 6 of 14
November 2, 2017
1.3.2 Line Termination Resistor
The RS-485 bus requires that the end-of-run device be terminated with a 120-ohm resistor. This is
accomplished by setting the LINE TERMINATION switch to “ON” if the MODBUS Interface Card is
the last device on the bus. Otherwise this switch should be set to “OFF”.
1.4 LED Indicators
Visual indication of Modbus activity is provided by a SLAVE RECEIVE (RX) and a SLAVE
TRANSMIT (TX) LED. Note that SLAVE RECEIVE indicates for all MASTER/HOST transmissions.
DWG NO. 20197 REV. B
I
N
O
U
T
MODBUS CARD
(TOP VIEW)
"OFF" POSITION
TO ADD ANOTHER
TMS/LC2000
WHT/BL (A+)
BL/WHT (B-)
SHIELD (SHD)
WHT/BL (A+)
BL/WHT (B-)
SHIELD (SHD)
2 CONDUCTOR SHIELDED
RS-485 COMM. CABLE
I
N
O
U
T
MODBUS CARD
(TOP VIEW)
WHT/BL (A+)
BL/WHT (B-)
SHIELD (SHD)
"ON" POSITION
FOR LAST
TMS/LC2000
END-OF-RUN
TX
RX
SHD
B-
A+
SH
D
B-
A
+
OFF
TERM
ON
TX
RX
SHD
B-
A+
SH
D
B-
A
+
OFF
TERM
ON
SHIELD WIRE SHOULD
BE CUT BACK AND LEFT
UNTERMINATED
THIS END ONLY
MODBUS MASTER
(EXAMPLES: BAS, BMS, PLC)
TERMINAL BLOCK
(SHOWN FOR REF.)
WHT/BL (A+)
BL/WHT (B-)
SHIELD (SHD)
SHIELD WIRE SHOULD
BE CUT BACK AND LEFT
UNTERMINATED
THIS END ONLY