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SIMATIC S5 / STEP 5

force variable of S5

Thread Starter: naga   Started: 12/9/2009 3:04 PM   Replies: 4

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  12/9/2009, 3:04 PM
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Dear all,

I wish to force a variable and as per manual Modifying the Value of a VAriable after the message staturs processing active, I pressed ESC once then screen shows operand and Force Process Image, but before I attempt to change the value Force fct not possible is getting displayed as message. Why so? Can I force flags and S values in RUN mode. For output forcing PLC must be in STOP mode Is it?

Regards,
Vijay 
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  12/9/2009, 3:40 PM
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Hi naga.

It's been a lot of time since i did this for the last time, right now i have no S5 software or S5 PLC to test but i remember that for forcing digital outputs (lest say Q0.0) you do not have to put the PLC in Stop mode, the only thing you have to do is to insert a BEU instruction at the begin of the OB1, in other words you have to avoid the PLC to execute the program.

As i said before is the only way i know, but maybe other guys have beter ideas.

I hope this help, good luck Rnf:lblSmileyTooltip_ .

Keep working!
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  12/10/2009, 8:50 AM
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Hello!

If you want force Q or I you have to do it by changing program. For example - for changing Input you have to add at the beginig of the OB1 for example:
"AN I0.0
=i0.0" - you will have I0.0=1 for all programm
for ouput, add at the end of OB1 (just before BE):
"AN Q0.0
=Q0.0" - you will get Q0.0 =1
I think it should work - it is because PLC routine works like this:
1.Check and seve in memory all input/outputs
2.Make program
3.Changing outputs
For changing flags you can use "force variables" from test menu - just
1.input flag which you want to change,
2.press "insert" to get online status,
3.press "escape" - after changing value of flag, press insert to confirm
it should work, I havent got online connection right now to check for sure, but I will soon have it

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  12/12/2009, 12:39 PM
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Thanks to both of you,

But what the message I am getting after Insert and ESC once is "Force FCT not possible" What does it mean. For Input and flags also I am getting this message.

And logically if I write program in OB1, it requires Downloading. Is it advisable to download the modifications, while PLC is in RUN mode.

Regards,
Vijay
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  12/13/2009, 1:33 PM
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Hello naga

it seems there is some confusion going on here, so here's my attempt to help.
To begin with, "Force Variables" in Step 5 is a bit of a misleading term. Your "force" is not a permanent force but rather a oneshot write of the signal into the PLC (and can or will be overwritten by your logic).
"Force Outputs" in Step5 on the other hand is a permanent force but works only when the S5 in in STOP (i.e. logic is not executed so nothing will overwrite it either).

As for your specific questions:

naga wrote:
But what the message I am getting after Insert and ESC once is "Force FCT not possible" What does it mean. For Input and flags also I am getting this message.

Both "forcing" functions have one thing in common, you can NOT "force" individual bits, only Bytes, Words or Doublewords can be "forced" and I wonder if that is your problem here. 

naga wrote:

And logically if I write program in OB1, it requires Downloading. Is it advisable to download the modifications, while PLC is in RUN mode.

Nothing wrong with downloading individual Blocks while the PLC is running, S5 and S7 PLC's are designed for this.

You'll can also find some more useful info about this in the Step5 manual (check what version you are using and do a search for it in https://support.automation.siemens.com)
 
I hope this helps

Cheers

fritz

The advice and opinion given in this thread is that of the author and does not necessarily reflect the views of I S Systems Pty Limited.
To find out how I S Systems can help you with your automation needs please visit www.issystems.com.au.
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