Modbus Device Troubleshooting

There are some tips for troubleshooting Modbus devices.

DANGER
HAZARD OF ELECTRIC SHOCK, EXPLOSION, OR ARC FLASH This equipment must only be installed and serviced by qualified personnel. Apply appropriate personal protective equipment (PPE) and follow safe electrical work practices. See NFPA 70E in the USA, CSA Z462 or applicable local standards. Failure to follow these instructions will result in death or serious injury.

This table describes how to solve issues with Modbus devices.

Issue	Possible Solution
No Modbus device can be detected on the Com’X serial line.	Open the Measurements Table main tab of the Com’X. If the Rx communication LED does not flash on the device, check the wiring integrity. If the Rx communication LED flashes on the device, but the Tx communication LED does not flash on the device: check that the device settings match the Com’X Modbus serial settings (Baud rate, Parity, and Number of stop bits). check that the Serial line polarization is set to Yes. check that the Serial line polarization is not activated on another Modbus slave device on the same serial line.
Some Modbus devices are missing on the Com’X serial line.	Check the Modbus addresses of the missing devices.
	Check that two devices do not have the same slave ID.
	Check that the settings of the missing devices match the Com’X Modbus serial settings (Baud rate, Parity, and Number of stop bits).
	Check that the wiring connections of the missing devices are correct.
	Check that the discovery range is large enough. The factory settings range from 1 to 10.
	Check that the wiring of the missing devices is correct.
No Modbus device can be detected downstream from a gateway.	Use the Diagnostic/Read Device Registers feature of the EGX to determine if the issue is between Modbus device and the EGX or between the Com’X and the EGX. If the issue is located between the Com’X and the EGX, check the IP address of the gateway. the EGX and the Modbus device, check that the Modbus device settings match the EGX serial port setup (Baud rate, Parity, and Number of stop bits). The combination (Parity = none and Number of stop bits = 1) of port settings is not supported by the EGX. Change to another combination.