User`s manual

Western Reserve Controls 1782-JDM User’s Manual
PUB 24.0
28
Problem: JDM operates on DeviceNet but does not seem to handle ModBus activity.
Possible Solutions:
1. Check the RX and TX LEDs on the JDM. A successful transmission will appear as:
• Brief TX LED flash
• Brief RX LED flash
• Both LEDs off
If the sequence does not appear as this, then there is a wiring problem.
2. If this is an RS485 link, make sure it is properly terminated. (121ohm resistor at each
end.)
3. Make sure the TX and RX, or SIG+ and SIG-, are not crossed.
4. Make sure your signal commons are connected.