SLC 504 to ControlLogix MSG on DH+

I have a SLC 504 that needs to read and write information to a ControlLogix Processor over DH+.

I researched this on the Rockwell Knowledgebase.

I was able to get the write message to work.

Error code (hex) :f2

"Invalid parameter; invalid data in search or command block"

The read message is configured the same way but is not working.

Per the Knowledgebase article they should be configured the same.

Link to knowledge base article:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/19945/related/1

Any ideas?

Thanks,
Tim

Can you post screen shots of your message configuration screen for us? Would help to see how they are setup. Both the read and the write.

Are you interlocking the messages so they don't attempt to execute at the same time ?

I agree that two similarly configured MSG instructions ought to work.

Are you using a Local message (just one ControlLogix in the target chassis, with the Default Slot number configured in the 1756-DHRIO) or are you using the Remote DH+ Addressing method ? Local is far easier to configure and troubleshoot.

Attached are the Read and Write messages.

I am simulating, so I initiate each message manually.

The SLC talks direct to the DHRIO in the ControlLogix chassis.

The routing table is set up...

ControlLogix Backplane Link 10
DHRIO Channel A Link 12
SLC Link 12

Tim

I would experiment with either an SLC Typed Read/Write command, or experiment with a smaller size.

The Instruction Set Reference says 103 words is the maximum size for a Channel 0 transaction. I don't know for sure if that applies to Channel 1 as well.

The reply from the ControlLogix suggests that the target address doesn't exist or can't accept the message. Usually you see this if the target array isn't large enough.

I'm baffled about why the Write works and the Read doesn't.

Originally I did this with 2 SLC's and it worked great...of course the message block was slightly different, but the size was the same.

Tim

It's likely that the problem is in the 1756-DHRIO or in the ControlLogix Map PLC/SLC Data Table function. It's a good datapoint that this does work between actual SLC-500 controllers, using the PLC-5 command type.

Well..I used the SLC as the target device when going SLC to SLC....but that did not work with the SLC to ControlLogix.
It seems that if the mapping was wrong the Write MSG would not work.
I just changed the Element size in the Read message to 60 and now the read works, when I go to 61 it errors.

Tim

It sounds like you've found the practical limit; now you can try to use two MSG instructions with smaller data sizes.

It doesn't make sense to me; everything I've read about the way PCCC messages are handled inside the 1756-DHRIO suggests you can send a 103 word message. Unless you have a compelling reason to pursue it, I'd just work around it.

Well...the only thing is...I have a lot of data to send.......with a 60 limit I will have a ton of message blocks.....for each 60 group......
103 was bad enough...
Tim

Well, that's a reason.

Have you experimented with Local DH+ addressing to see if that makes a difference ?

When I've tried to troubleshoot other people's DH+ networks, I've found it far easier to understand (and document) the Local DH+ addressing mode and the DHRIO default slot number method, rather than wading into the DHRIO routing table.

Well...if what you mean is to set the MSG block to local rather that remote...I just did that and the same 60 limit exists.

Tim

For what it is worth, related to this thread, I prefer to only use "Read" messages between PLCs.

I have worked on large systems that "evolved" over a number of years, usually involving several systems integrators, and the net result was that the messaging area always got "cruddy" in the process.

Seeing data-table or tag values values changing in a PLC and not being able to find out where those values are coming from can be a real PITA if those values are being written by another PLC. I have even seen instances where two PLCs were writing to the same destination in a third (table overlap).

If you standardised on using Read messages, the cross-reference would show the relevant MSG instructions, and you can go look at the configuration of those to see where the data source is.

Of course I understand that sometimes you cannot change the code in the destination PLC, and you are forced to use MSG Writes, on those occasions I would add documentation to the target PLCs tags/data table locations to show where the data is coming from.

Valid point.

In this case, however, the SLC processor run the machine, the ControlLogix is strictly used for Recipe backup.....thus the initiation of the read and write command is generated manually from the local PanelView at the machine.

The only data in the ControlLogix will come from these machines.

Thanks,
Tim

Message Buffer

I created a READ and WRITE message in a ControlLogix program that reads data tables in a SLC 5/04. I used "SLC Type Read" and "SLC Type Write" messages. Due to "Buffer" words, the data table in the SLC had to be twice as long as the message array in the ControlLogix program.
For instance, I used a tag array of "Fr_SLC[0] thru Fr_SLC[9]" for my ControlLogix READ message. In the SLC program I had to create a data table N7:20 thru N7:39. The odd words are buffers and cannot be used.
So, in the READ MSG, N7:20 is read into the ControlLogix "Fr_SLC[0]", N7:22 is read into Fr_SLC[1], N7:24 is read into Fr_SLC[2], and so on.

In the "Write" MSG in the ControlLogix program:
To_SLC[0] writes to N7:40
To_SLC[1] writes to N7:42
To_SLC[2] writes to N7:44 and so on.

Therefore, the data table in the SLC program needs to be twice as long as the data table in the ControlLogix message READ or WRITE. If the data table in the SLC is not long enough, you will get an error.