Prosoft MVI69-MCM

Dear all,

I am desperate for some help with a Prosoft DVI69-MCM MODBUS module.

Details:
Prosoft DVI69-MCM MODBUS module set up as slave with a CompactLogix PLC 1769-L33ER PLC. I have added the Prosoft add-on instructions from their website. The Master is a third party machine that is trying to write and read information from the Prosoft module.

I believe the system is set up correctly because the Master can successfully read information from the slave. My problem occurs when the Master tries to write data back into the read holding registers of the Prosoft module.

Part of the requirement of the Master is that it needs to see a string of 'X' characters in the read holding registers before it will write any information. My problem is that when I try to write information into the read holding registers they reset back to '0', which means that the Master faults saying it does not have 'write permission'.

I believe the add on instruction AOI69MCM supplied by Prosoft is where the read data is being reset back to '0' but I am not sure why it has been set up to do this. I have tried setting the module up as a pass through slave but I have the same problem. I also know its not the Master resetting the read holding registers because when I unplug it the I can still see the data going back to '0'.

I have been trying to set up this system for some time with no luck, so any help would be very much appreciated.

Thanks

I've run into this sort of application problem with the MVI56-MCM module.

What's going on is that the module doesn't really have a read-and-write data table like a PLC would.

Instead it has a database element range (and corresponding Modbus address range) that gets written to by the CompactLogix, and a different database element range that gets read by the CompactLogix.

There's no easy solution; this is just the way the Prosoft modules work, with separate database ranges for data that will be "read" and a different database range for data that will be "written".

The Modbus pass-through slave feature is the standard solution to this problem. Your logic accepts the Modbus Write commands into the passthrough data area, and applies those to the CompactLogix internal tags which then get written to the MVI69-MCM, and are read by the Modbus Master.

Prosoft tech support is very good at this sort of thing, so make sure they're involved in helping you out.

Thanks for the response Ken.

I have tried setting the module as a slave pass through but an still having the same issue, is there a different add-on instruction required for the module when it acts as a pass though slave?

I have also written to Prosoft with the issue and am waiting on a response

I am starting to wonder if this is at all possible. I have been told however that a similar system has been set up overseas but I can get any info on how it was achieved.

If I find a solution I will repost because this has been frustrating to say the least.

Thanks

Maybe you should consider using a gateway instead...
http://www.anybus.com/support/support.asp?PID=172&ProdType=Anybus X-gateway


My 2 cents

My recollection is that the Modbus pass-through slave mode requires you to deal with the incoming Modbus messages yourself.

Instead of applying a Modbus Holding Register Write to some part of the MVI module database, the Prosoft module presents the essentials of the Modbus message in specific data registers, and you have to decode them and move that data yourself.

I don't have enough time available to write up an example that would be any better than Prosoft's. If you can post details of your program (or at least the parts that deal with the MVI69) and the Prosoft Configuration Builder file, folks might be able to provide some additional input.

Coop..

Please post back here if you're still having issues. As Ken stated, reading and writing to the same address can only be achieved via pass-thru. If you have the correct ladder/AOI loaded, the only thing you should need to do is to set the port to Slave Pass Thru.