MODBUS RTU Master on OMRON CPM2

[Marke]

Hi

I have a requirement to controll soft starters and VFDs using the OMRON CPM2 series PLCs.
This will require the CPM2 to act as a MODBUS RTU master.
Has anyone done this before?
Any pointers before I start from scratch would be wonderful.
I will have to had code the TX commands into strings etc. Why reinvent the wheel if it is available?

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[artecerv]

Hi Mark,
MODBUS RTU (serial) could be extremely slow depending on cable lengths and number of nodes. I wouldn’t recommend it for control (monitoring perhaps) …
Unfortunately, I have not experience with Omron PLCs, so I can’t help with that … Can you please explain whether you are writing the protocol yourselves or using Omron’s.
Regards,

 

[Marke]

Hello artecerv

Thank you for your reply. Fortunately, this application does no require high speed and the plc will be close to the drive or starter. The major requirement is for monitoring with some control.
Looks like I will have to write the protocol myself as I have not been able to find a MODBUS RTU master to run on the CPM2.
Thank you for your comments,
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[artecerv]

I suggest you to visit this site:

http://www.plcs.net

It is the biggest PLC site in the net (at least that I know of) ... surely you'll find there Omron’s PLC users.

Personally I wouldn’t try to write my own protocol (except you are doing it for academic purposes). Customized communication programs require thorough testing and event with that it is hard to predict how the hardware will behave (I learned that the hard way with the A-B Basic module years ago).

Good luck...

Regards,
Leonardo

 

[Marke]

Hello artecerv

Thank you for your comments.
The project is for a client, definitely not for academic purposes. I have done this sort of thing plenty of times before with dedicated processors, but never with the OMRON CPM2 plc. - bit of a learning curve to go through, but that is not a problem.

Have a good day,

Mark Empson

http://www.lmphotonics.com

 

[dstable]

Hi there Mark

http://forums.mrplc.com/index.php?download=512

Check out the above link, this may help, re your omron modbus application

regards

Derrick Stableford

 

[Marke]

Thanks Derrick, I'll check it out.
Best regards

Mark Empson

http://www.lmphotonics.com

 

[OldPfart]

I do not know whether it was you Marke or someone else that I referred to my download at MrPLC.com. The ladder version is slave only but should be able to be adapted to master.

The simplest way is to use the CJ1M with an SCU comms unit. Use CX-Protocol to download the Modbus protocol available at that site. Then simply a couple of instructions in ladder and it all happens.

Hope it helps.
BobB