GE 90/30 modbus card

If I want to talk to a modbus slave at address 1 to register 037 using a Horner RTU master communication module in A GE 90/30 PLC has any one got any programming examples for this plc.
Thanks
Pauly

There are ladder logic examples in the manual m007607.pdf available from the Horner website

http://www.heapg.com/Documentation/90-30 and 90-70/HE693RTM705 & HE697RTM700 & HE693OIU037/

You need to use a COMREQ instruction, and that's not the most straightforward thing to do. Make sure that the COMREQ instruction is triggered by a one-shot. If you have problems, post your code and I'll try to help troubleshoot it.

modbus GE PLC card

With respect to the above reply, I am confused as to why we need a comrequest when we are using a dedicated modbus card?
Does the card not handle this function?

RTU Comm_Req

Yes, the RTU module handles the RTU communications. The Comm_Req is how the CPU communicates to the module.
"You can't get there from here, you need to go there first."

RTU communications is master/slave. The master initiates all communications, the slave merely responds. If the PLC were an RTU slave, no ladderr logic would be required. If the PLC is to be the RTU master, the COMREQ is necessary to tell the module to send a request for data to the slave device.

Pauly,

I see you've posted a request for help on another forum. The offer I made in post #2 of this thread still stands. Attach the pertinent ladder logic and the configuration details of the Horner module, and I'll take a look at it. Another set of eyes may catch something that you're missing.

There is also a heap of ladder to set up so that COMREQ knows the number of the unit, baud rate, stating word, number of words etc. Bit daunting first time but it works.

The request packet reminds me some what of explicit messaging with Device Net. One number wrong and it will not work. You have to tell it exactly what to do.

Once done for the first time it is quite easy. Just keep and modify your code. I would also suggest that you comment it well so that you can easily understand all items of information and what they represent. Makes it a lot easier when you have to do it again in 2 years time.

Hi I am a Novice for this GE RTU Master Integration of this HE693RTM705 . Currently I am doing a Modification work for an old System. Does anyone have any sample program either in Ladder Diagram / Structure text or C program . C program if possible cause there is a lot of repetitive action.


The Previous communication program of the RTU Master they wrote it in C. But i could not understand it , course there is no proper comment and definition written in the program.


Anyone please help
thanks

Pauly, You might try this document.

http://support.ge-ip.com/support/re...aging/DOCUMENT/0/DO272/en_US/1.0/GFK2220C.pdf

It may help clarify some things. The Modbus Comm_Req may be intimidating at first but once you get how it works it will get easier. I would take Steve up on his offer and there are many eyes here to help.

khaiseng82 said:

Hi I am a Novice for this GE RTU Master Integration of this HE693RTM705 . Currently I am doing a Modification work for an old System. Does anyone have any sample program either in Ladder Diagram / Structure text or C program . C program if possible cause there is a lot of repetitive action.


The Previous communication program of the RTU Master they wrote it in C. But i could not understand it , course there is no proper comment and definition written in the program.


Anyone please help
thanks

Click to expand...

A lot has changed since 2004, you may want to try starting a new post next time, so to not confuse me.

Here is the manual for your Horner module, now. It should answer your questions, if not come back with specific questions.
Scroll down or search (Ctrl-F) for your module:
http://heapg.wpengine.netdna-cdn.com/oldsite/manuals/Documentation/90-30 and 90-70/

Thanks to all guys, i will try it out

Regrettably....once you have it working, it will make sense and you will be a pro.

COMMREQ logic is always hard to figure out first time.

Huge sense of accomplishment to get a COMMREQ to work.

..

Comm Succeeded but need to perform Mod bus Switching

Dear All


Thanks for the help of you guys, I have successfully did the Modbus communication. And it is Communicating with the Slave

But i have still one problem remaining to solved

I have one 5 slot rack using GE CPU 350.

2 pcs of HE693 RTM 705 is connected to the CPU 350

My control phillosophy should be like that :

1.Only the 1st card HE 693 RTM 705 should be communicating with the Slave.

2. While the 1st one is working the 2nd one should not be turned on

3. When the program detect there is a failure of the 1st cad HE 693 RTM 705 fails it will switch automaticlally to the second Card.

4. the Second card will be communicating with the Slave.

5. The program will always check the status of the 1st card RTU Master.
If the 1st RTU Master card is Ok it will switch back to the 1st card and
then shut down the 2nd RTU Master Card.

I have checked the previous program written in C 10 years ago by another guy. He is using some kind of rotate function to switch it between module and port. But i can't fully understand what he write and how he do it.


Any expert here can provide advice or example how to do it
Cause i have been:smas:figuring some time how to do that.