Troubleshooting of modbus communication to a serial device connected through an EGX100 or EGX300

Issue
Troubleshooting of Modbus communication to a serial device connected through an EGX100 or EGX300

Product Line
EGX100, EGX300

Environment
EGX web server, dip switches, and wiring

Cause
Physical wiring, dip switch configuration settings, and the EGX web server configuration must be correct in order for correct communications.

Resolution
Wiring
The EGX supports both 2-wire and 4-wire configurations provided dip switch settings are correct and serial port settings match. The EGX installation guide includes details about wiring 2-wire and 4-wire systems. If a 4-wire device needs to be connected to a 2 wire configured EGX, bridge RX+ with TX+ on the device, and connect this to the Rx+ connection on the EGX. Similarly, bridge RX- with TX- on the device, and connect this to the Rx- connection on the EGX.

Dip Switches
The EGX dip switch configuration for the RS-485 Biasing and Termination should be set to match the system as described below.

Figure 1: Dip Switch Configuration For 2 or 4-wire Devices

EGX web server configuration
To access the configuration section for the EGX serial port access the EGX web server by typing the IP address into a web browser. Navigate to Setup->Serial Port


Figure 2: Serial port configuration on EGX web server

• Ensure the Physical Interface is appropriately set for 2 or 4-wire.
• Ensure the Baud Rate matches the rate that the serial device is configured for.
• Ensure the Parity matches the parity that the serial device is configured for.

Access the Device List located in Setup->Device List on the EGX Web server

• If the Unit ID of the meter trying to connect is not entered into the Device List of the web browser, then add it.

NOTE: Unit ID is not recommended to be set to 100. The reason being that Unit ID 100 is reserved for Modbus TCP connection.

Verifying Successful Communication
The 3 screen shots below displays what the correct configuration will result in.

Read Registers from EGX web server :
Go to Diagnostics->Read Device Registers

Figure 3: Reading device registers on the EGX web server

Read registers with mbmasterv21m3:

Figure 4: Reading device registers with mbmaster

Read registers with Modbus Tester:

Figure 5: Reading device registers with Modbus Tester