Symax 400 Mystery Register

[nmontev]

We have a demineralizer running on a Symax 400 PLC. The PLC is connected to a Cincinatti Display serially. This system is a late 80's early 90's vintage. There are several valves that open and close based upon a specific step of a sequence.

The issue I have is I cannot find what is turning on and off bit (2500/08)= SV-10608, Rung 387. (This is just one of many valves that are not responding as desired, but I think if I understand one, I can get the rest.) I would expect something to be forcing different numbers into the 2500 series register that would correspond to the valves that should be open in a given step of the sequence. (2500/01 = SV-10601....2500/08 = SV-10608....) I cannot find anything manipulating the values of register 2500 or the individual bits for that matter.

Rung 372 contains the drum of the sequencer. The index is kept in (S2300). I have been looking here to see if anything from this is manipulating my 2500 register, and if it is, I don't understand how.

Given the problem that I can't seem to locate anything in the PLC program that is manipulating register 2500, we looked to the Cincinatti Display. The plant has found the code we believe to be in the display, and most of the items line up, i.e 903-01 of the Cincinatti Display has the same description of 903-01 in the Symax. The issue is I don't see anything referencing 2500 in the display program either.

With all of that background information, can anyone tell me what is manipulating bit (2500/08) of my program? I have attached a printed file of the Symax Code, the Cincinatti Display Code, and a spreadsheet with the expected operation of the various valves. Any direction would be much appreciated.

 

[George Graziano]

Have you searched for the whole register S2500?

George

 

[nmontev]

I have found in the register descriptions near the bottom of the code a list of outputs starting at register 2312. When I look at the program live, the values in 2312 look like the valves that should be open in my first step. 2318 looks like the valves that should be open in the second step etc. We are running a test to verify that these are the values getting pushed into 2500. My issue is still the same though. I don't understand how 2312 or 2318 are getting pushed into 2500. If my theory works, I can make the changes I need to correct the program, but I still won't understand exactly how it works.

 

[nmontev]

My guess was correct. We found a book that defines the sequencer block in rung 372. The 5th offset of the listed register contains the desired output location. Register 2305 points the outputs to register 2500. That's what I was missing.