SLC 500 Program Checksum

  • Thread starter Joe Jansen/ENGR/HQ/KEMET/US
  • Start date

Thread Starter


Hey all,

I have a SLC-5/04 processor that is controlling a process machine. There
are several parameters that must be set up prior to use, but can go days
without change. Because this is a new group of machines, we are doing a
lot of development. There arises situations where one of the technicians
downloads a program, overwriting the process parameters. Since it is not
possible to download program without data, the parameters need to be
re-configured before start-up.

As you may guess, this sometimes fails to occur. I have been, therefore,
commisioned with finding a way to determine if a program has been
downloaded. One solution I am investigating is finding a way to access the
program checksum as displayed in RSLogix. Can I get at his number from
inside my ladder file? I have already tried using a version number in the
data files, but if this isn't changed, it doesn't work. I have considered
a first-scan type latch, but this also is unwanted due to occaisional power
cycling.... If I can get the checksum number, I can save it on the HMI
computer. If there is a mismatch, we can prompt the operator to re-run
their setup procedure.

If anyone can tell me how to get at the checksum, let me know. I will post
the resulting code on the PLCArchive. I cannot find it just looking at the
status data, but I am hoping to find a way to index past the end of a file
to get at it, or something similar if needed.


--Joe Jansen

darcy oldfield

if you can store the checksum number in the HMI why not store all your saved data in the HMI computer.
another solution is if the data being used is a constant couple of numbers then hard code it in the logic so that the operator would only pick say a part number then the apropriet settings would be moved to the desired areas.
The technicians are doing a very risky thing by just going to the machine and downloading. The proper proceedure for them should be to upload save the upload then download it. The should design the change then implement it into the uploaded program.
If you wanted to control access to the program you could put on the password protection which would only let people with the password into it.
Perhaps the best way for your aplication is a software package from Rockwell called RSguardian. RSguardian can monitor and log PLC uploads, downloads, and can be programmed to make schedualed back-ups of the programs. This program call for a computer to be hooked into the PLC at all times though.
Joe Jansen:
> Since it is not possible to download program without data, the parameters
> need to be re-configured before start-up.

> As you may guess, this sometimes fails to occur.

Just a random suggestion, but - add a ``parameters verified'' parameter
into the downloaded data, and check it in the program? As long as it's 0
(false), the program ain't allowed to run.

The setup procedure can set it to 1 (true) when it finishes.

Jiri Baum <[email protected]> the MAT LinuxPLC project at

Alan Rimmington

If you send me your e-mail I will send you four lines of code that will record if the SLC has been in prog mode or if the download is fresh, it ignors power cycles.


[email protected]

Michael Griffin

How about a copy for the PLC Archive? I'm sure other people would
like to see this in future as well.

Michael Griffin
London, Ont. Canada