How This Works - VSCOM ModGate Plus User Manual

8 Example Configurations
The remote ModGate Plus Gateways R (R2, R3, ...) are in default configuration for simplicity.
Here Allow unknown clients is enabled, otherwise a TCP connection to the ModGate Plus Gate-
way L would be required.

How this works:

The serial Master on the existing serial line now connects to the ModGate
Plus Gateway L also; the Master sends requests to many Modbus IDs. When such an ID is not
configured in Gateway L, the ModGate Plus simply drops the request. The target is on the serial
line, and will eventually send the response.
But when this ID is configured in Gateway L, it forwards the request to the responsible Gateway R.
Since the TCP connection is configured as TCP (Gateway), the target Modbus ID is retained (not
replaced by 255/0xFF). Now Gateway R forwards this request to its own serial line, where the
remote Modbus/RTU device gets it. The response is sent on the serial line, forwarded back from
Gateway R to Gateway L, and then to the original serial line and to the Master. The communication
cycle is finished with this final forward. The figure 36 shows such a setup.
June 2018 ModGate Plus User Manual 45