User`s manual

Western Reserve Controls 1782-JDM User’s Manual
PUB 24.0
15
3.3 Serial Port Connectors
Your ModBus device(s) are connected to the JDM via 3-wire or 5-wire communications cable. See your
ModBus device User Manual for details on the specific connection.
Table 3-3 RS-232/485 Connector Signals
Pin # RS232
Signal
RS485
Signal
Designator
1 Receive Signal - SIG-
2 Transmit Signal + SIG+
3 Ground Ground GND
Table 3-4 RS-422 Connector Signals
Pin # Designator
RS422
Signal
5 TX- Transmit -
4 TX+ Transmit +
3 GND Ground
2 RX- Receive -
1 RX+ Receive +
3.3.1 RS485 Network Termination (1782-JDC-2)
An RS485 system typically requires a terminator resistor at each end of the line. Many
products may have an optional terminator built into the product. The JDM does not. The typical values for
the terminating resistor are:
• 100-120 ohm
• 1% metal film
• 1/4 Watt
This is similar to the termination requirement as for the DeviceNet link (121 ohm), so the same
resistors may be used in many applications. It is the user’s responsibility to determine the appropriate
terminations for the application.
Note: 1782-JDM-2 products shipped with date code “0338” and earlier may have an internal 220-
ohm terminating resistor installed. If you have any questions about this, please contact WRC by
phone or at [e-mail].
3.4 Power Requirements
3.4.1 Device power
The JDM is powered directly from the DeviceNet connection 11-25 Vdc power supply. The JDM
consumes 90 mA of current at 24 Vdc, or ~2 Watts, typical.