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The RS-485 signals are located at the 3.81 mm 6-pin pluggable terminal block on the top
side of the mounted unit (refer to Figure 2.1, "Location of connectors" ). The following
table and picture shows the pinout:
Pin
3
RS-485
4
5
6
7
8
Table 3.3: RS-485 connector pinout
• Line termination is required and is typically done with a 120 Ohm 1/4 W resistor. For
RS-485 operation the bus must be terminated at both ends.
• Maximum number of RS-485 nodes without repeater is 32.
• Stub connections off the main line should be avoided if possible or at least be kept as
short as possible. Stub connections must not have terminating resistors.
• Maximum cable length to 1200 m (4000 ft).
• To assure a high degree of electromagnetic compatibility and surge protection the
cable should be twisted pairs and shielded. An additional cable conductor or pair may
be used for the GND reference.
Do not connect the cable shield to the GND pins! Use an external chassis ground
connection to terminate the shield.
Wiring the RS-232 Modbus interface
The RS-232 Modbus interface can alternativly be used for serial communication to a
Modbus master device instead of RS-485. The use of the RS-232 interface must be
configured using the web interface (See the section called "Configuring serial line
Modbus"). The GCP-MG is a Modbus slave device.
The RS-232 Modbus connector is a male 9-pin D-sub type located at the bottom side of
the mounted unit (refer to Figure 2.1, "Location of connectors" ). It has industry standard
UMGCPMG-2201
Signal
Function
GND
Modbus Common
D+
Modbus D1
D-
Modbus D0
reserved, must be left unconnected
reserved, must be left unconnected
reserved, must be left unconnected
Installation
13
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