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Why am I unable to modbus master an ION7700 via modbus TCP?

Published date: 16 June 2020

When attempting to modbus master an ION7700 over ethernet using port 502, data shows up as [n/a] on the master device (ION7550/7550RTU/7650/8600/8650).  Modbus mastering via the serial ports is still successful.

Product Line:
Modbus mastering an ION7700 via Modbus TCP
The ION7700 does not support port 502. As a result, it is not possible to modbus master the ION7700 via ethernet alone. 
Though there isn't a full resolution to this issue, there is a workaround if the ION7700 has unused serial COM ports. 

On the ION7700:
1. Change the protocol of COM2 to Ethergate.
2. Change the protocol of COM3 to Modbus RTU. Take note of the Unit ID of COM3 as you will use it on the master device.
3. Wire the COM2 and COM3 ports together: Wire "+" to "+", "-" to "-", and "SH" to "SH". 
On the master device:
1. Edit the Modbus Master Options Module>TCP Connection 1: <ip address of the ION7700>:7802/RTU
(Note the special /RTU modifier. This tells the master device to use Modbus-over-TCP, like a serial connection, instead of the proper ModbusTCP.)
2. Edit the Modbus Master Device Module>Slave Addr: <Unit ID of COM3 on the ION7700>

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