RSLogix 500 program

taib1800 · Sep 30, 2004

I have written my first RSLogix 500 program. When the PLC processor is powered up, bit S:1/15 is suposed to be turn on for only the first program scan.

In my case it is turned on all the time and I am not able to run the rest of my program because it deletes internal memory files all the time. Can anybody please tell me what is wrong.

Allen Nelson · Sep 30, 2004

First start with the obvious

Do a cross-reference on S:1/15.
- Are you writing to it anywhere (OTE, OTL, even OSR)?
- What about the word S:1? Any MOV's, COP's or anything like that?

And, just to start looking for the weird stuff, is S:2/3 set?

paraffin power · Sep 30, 2004

Is the plc still 'running'? It's not going into fault on the first scan and it looks like the S2:1/15 is staying on?

pp

taib1800 · Sep 30, 2004

please help

As you can see, I don't have a lot experience. During my first scan I am doing FLL command which erases anything what I had in my B3:0 word.The problem is that it keeps erasing all the time. It looks like the processor doesn't recognize it as command for the first scan. My cross-reference on S:1/15 shows just a 0 for a value.
How do you set S:2/3.

thanks

JesperMP · Sep 30, 2004

Try to look at the cross reference for both S:1/15 and S:1.
There should be no WRITES to any of these two addresses.

Why do you want to set S:2/3 "allow indexing accros files" ?

You could zip and attach the .rss file and let us have a look at it.

Allen Nelson · Sep 30, 2004

Re: please help

taib1800 said:
During my first scan I am doing FLL command which erases anything what I had in my B3:0 word.The problem is that it keeps erasing all the time.

So your logic looks like this:





   S:1/15     +--- FLL ------+

----| |-------| Source:    0 |

              | Dest:  #B3:0 |

              | Length:    1 | <<-- May be different 

              +--------------+

If not (for example, you have -|/|- S:1/15), then you may have a problem with your logic, not the PLC.

My cross-reference on S:1/15 shows just a 0 for a value.

That doesn't sound like a cross-reference, that sounds like a "View Data Table". A cross-reference will show you where in the program S:1/15 is used. (Unless it is only used on Rung 0 of LAD 2, then it may say "0")

How do you set S:2/3.

Don't. Just check under the Main Tab of Processor Status and see if "Index across Data Files" is "No" (should be) or "Yes".

taib1800 · Sep 30, 2004

S1/15

Here is my programm. Thanks.

taib1800 · Sep 30, 2004

S1/15

Here is my programm. Thanks.

paraffin power · Sep 30, 2004

Either jump to a different subroutine on the first scan (jsr) or do what Allen said.
The LBL will get processed every scan, not just when you jump to it.

pp

grs · Sep 30, 2004

Your initialize subroutine still gets called and zeros the files whenever the processor gets around to scanning file 2 rung 6 (IE, every program scan).

Why not just use a rung like XIC S:1/15 JSR 15 instead of the JMP and LBL combinations?

*Edit: just one minute too slow, PP beat me to it

Allen Nelson · Sep 30, 2004

Well, that's easy.

So here's what you've got:



     S:1/15     Q2:0

-----| |--------[JMP]



<snip>

    Q2:0       U:15

---[LBL]-------{JSR]

So on the first scan, the all the code between the [JMP] and the {LBL} won't execute, and you'll do your "Clean B3 file" subroutine.

But on the next scan, there's nothing that's going to stop you from re-executing the JSR instruction. The [LBL] is only a label, it doesn't have any logic behind it.

A more effective method would be to remove the JMP/LBL pair, and write you first rung like so:



     S:1/15     U:15

-----| |--------{JSR]

That will do what you want.

Slow. Too slow. Got beaten twice.

paraffin power · Sep 30, 2004

I've obviously got less work to do than you two

taib1800 · Sep 30, 2004

my program

Thank you very much Allen. My programm works now thanks to you. Thank you one more time Allen.

RSLogix 500 program

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