I am starting to understand at least one MC-protocol or MELSEC "module" hast to be installed/activated on the PLC to enable communication.
When I query the PLC with the magic "Detect Now" button in the GX Works "Ethernet Configuration (Built-in Ethernet Port)"
In the "Host Station" column of the module list there is only one item "Module With No Profile Found" with Protocol UDP.
What Ethernet software module should I add to the PLC config for PLC to respond to MELSEC commands?
How do I write the added setting back to the PLC without affecting anything else?
Enabling the MELSEC protocol
At lest this forum can be used as a cloud storage for documentation answering my own questions:
Dear Flodis, maybe you can find useful information in the MELSEC-L CPU Module User's Manual (Built-In Ethernet Function) - Page 38?
This is what I learned:
MELSEC protocol and MC-protocol is not he same thing.
MELSEC is a proprietary Mitsubishi protocol
MC protocol or SLMP is the documented protocol
The protocol is installed as a module in the PLC ethernet config
Each module called MC/SLMP has an IP port defined
Each port allows one active IP connection at a time
The ethernet config allows for a total of 16 modules
It is important to keep a few MELSOFT modules as GX Works may not be able to connect
MELSEC Communication Protocol Reference Manual
In GX Works it may look like this. Notice the checkbox close to Ethernet Conf . button that offers two ways to defines ethernet modules for the protocols to enable for the PLC bult in ethernet module.
In this module configuration view the module of interest is called MC protocol and offers a port number.
In the more advanced ethernet config view the "MC Protocol" module is now presented as "SLMP Connection Module"!!!!!!!
This offers great confusion and takes a while to figure out.
Once the module config is written to the PLC it should respond to MC-protocol requests.
Notice requests can be either ascii or binary and is selected using the checkbox on the ethernet config main screen.
Do not forget to disconnect from the PLC TCP socket when access completed as it offers only single connection per port.