RJ71C24 Modbus RTU

[rikitech01]

I am currently working with an iQ-R R08CPU PLC and using the RJ71C24 module for communication with a Modbus RTU device. At present, communication via "Simple Communication CPU" works smoothly without any issues.

The problem occurs when I want to add another slave device to be read. The "Simple Communication CPU" configuration requires the PLC to be reset.

How can I communicate with Modbus RTU on the iQ-R so that I can perform an online change? Currently, the PLC cannot be reset due to an ongoing sequence.

[Parky]

I don't think you can as this is not like on-line change of the user program but update of the intelligent cards, these require the PLC to be in stop.

I'm not an expert on the later hardware & as this has been set in the card flash, however, I know on many older systems before intelligent cards were a thing the configuration was done by moving data into the buffer memory of the card with TO/FROM instructions or the Un\Gn function.

This may still be availlable i.e. write to the BFM's,  see this manual

goto Mitsubishi website & search for "sh081251eng" this shows the list of buffer memories

To do it this way in the user program if possible would take a lot of work & may still need a re-boot at some point.

There are some things you would need to think about, the BFM memory (8.5K of it) will be flash memory & as this has a limited write cycles then setting these is best done on first scan pulse so it is only written once on re-boot. (or a transition of a bit forced by GXworks).