SLC Comms Testing

andy_1983

Member
Join Date
Mar 2018
Location
uk
Posts
76
Hi,

I’m just after a couple of pointers on testing comms between SLC PLCs in a test environment (i.e. not on a live plant).

For a typical scenario I want to test 3 x SLC 5/05 CPUs that all talk to each other. These have all been upgraded from 5/04 CPUs - so the code is fine and I just want to check the new MSG instructions are all coded up ok and working.

Firstly, I thought I’d be able to test these using RS emulate with all three PLCs loaded in - and I’d be able to see them talking between each other in the emulator. A bit of reading around suggests this isn’t possible…. Could someone confirm? Ive only used RS emulate a couple of times a long time ago, and was only using one Program at a time.


If I can’t use emulate - then what I’ve always done is put 3 x four slot racks together with a test CPU in each. I delete out all the code with I/O addresses in, so each program goes into a 4 slot rack - rather than having to assemble all the I/O cards and extension racks.

The above works ok, but I wondered if there were any good ways of testing the comms without having to either assemble a load of test I/O or delete the code out so that it goes into short test racks?

The testing is needed because I have a short window in which to take out the 5/04 CPUs and put in the 5/05s - and I don’t have time to be debugging coding errors on the changeout. I’ve already been caught out with the need to delete and reimplement the message instructions and of course the bigger data table allowance required in a 5/05



Thanks
Andy
 
Last edited:
I would be very surprised if RS Emulate worked for this. And I'm not sure I'd entirely trust the results if it did.


To avoid deleting code, go into the Processor Status file, "IO" tab, and turn off the slot enable bits (S:11 and S:12).



The code will execute without processing the IO modules. You can also toggle the input bits and see the output bits change. It just won't try to read the input modules into the data table or write the data table to the output modules.
 
I can confirm that RSEmulate 500 will emulate the Channel 0 serial port, but not the Channel 1 Ethernet port.

>I'm not sure I'd entirely trust the results if it did.

Of all the things that are difficult or impossible to emulate, embedded TCP/IP stacks and hardware are high on the list. If you want to be sure that controllers network properly together, you need real hardware for those controllers.

I agree that the best way to test this system to give yourself the highest confidence is to use test chassis and real SLC-5/05 controllers, and disable the I/O modules.

The usual problem I encounter is that your test chassis need to be as big as, or bigger than, the user program calls for. You can't have 7/10/13 slot chassis in your application but use 4-slot chassis for testing.

It's been a while since I had to try that, but it's a strong recollection.
 
On Ken's post, as he stated, you can disable I/O so it ignores it, but believe you will need a rack that has at least the number of slots for the I/O you have, I have never tried disabling I/O modules on a 4 slot rack when a 7 slot is needed so don't know if it is possible but I doubt it.
 
As a test, I modified a working program for my test bench 5/05 by changing the 4-slot rack to a 7-slot rack and putting some random modules in the extra slots. All modules are disabled. Upon transitioning to Run mode, it threw fault 0x56, "The rack configuration specified in the user program is detected as being incorrect."


With it properly configured for a 4-slot rack and all of the configured IO modules removed and disabled, it goes to Run mode no problem.



I have not tested it with a larger than expected rack, but I suspect it would not be happy.
 
Thank you for your thoughts guys - points noted!

It’s a shame they didn’t come up with a simple feature to disable racks as well as I/O slots, still they’ve managed for 30 years without it.

Andy
 

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