Intelligent Technologies Modbus to QCPort Adapter Manual
January 2006
MN05002002E (C)
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Page 39
Modbus Pass-Through
Connect Modbus Slaves to Channel A or B
When one or both of the QCPort channels are reconfigured for Modbus, it will be required
to wire the Modbus communication wires to the proper pins. If Channel B is used for the
Modbus Pass-Through, the desired port if also using QCPort, then it is recommended to
use a D77E-QPLR as the interface between the Modbus network and the D77D-EMA.
Connect a standard QCPort interconnect between the Channel B of the D77D-EMA and
the D77E-QPLR, apply power to the + and – from a 24Vdc power supply. It is required to
power Channel B externally since the channel is electrically isolated from the D77D-EMA
and requires power to operate RS485 circuitry. The terminal block on the D77E-QPLR
will have connection points for connecting the Serial Modbus RS485 connections; the
connections are A, B and (-). Modbus needs to be terminated with 100 ohm resistors.
Table 38: Modbus Wiring for Pass-Through
D77D-EMA
CHA
CHB
D77E-QPLR
P-
P+
-
+
A
B
-
+
P-
P+
-
+
D77E-QPLR
P-
P+
-
+
A
B
-
+
P-
P+
-
+
QCPort
Device
QCPort
Device
Modbus
Device
Modbus
Device
A
B
A
B
24Vdc
24Vdc
