Alternate function in S7??

Dariusch

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• May 15, 2005

• #1

Hi.
How can I make an "alternate" function and toggle the Q on/off in a Step7??
Is there a function to use or do I have to make it myself. If so, is there an easy way of doing that.??

see attach pic.

Thank you

Dariusch

 

Ken M

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• May 15, 2005

• #2

Hi there,

Try this previous thread -
http://www.plctalk.net/qanda/showthread.php?t=13204

Regards

Ken

 

Dariusch

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• May 15, 2005

• #3

Thank you!

The code for the FC you have listed is great.

Dariusch

 

Amr Hassan

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• May 15, 2005

• #4

u can use this


a i0.0
fp m0.1
= m0.2


a m0.2
an q0.0
s q0.0
r m0.2

a m0.2
a q0.0
r q0.0

 

Dariusch

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• May 16, 2005

• #5

Hi Ken

Ken M said:

Code:

A #TRIGGER
FP #ONESHOT
X #TOGGLE
AN #INHIBIT
= #TOGGLE

Stick this in a Siemens FC with TRIGGER, ONESHOT and INHIBIT as BOOL IN parameters, and TOGGLE as the BOOL OUT parameter. This gives you a flip-flop plus an inhibit switch, all in six lines of code. Take out the inhibit if you don't want it, and now we are five.
The secret's in the 'X'.

Regards

Ken

Click to expand...

If I write it in a FC it wont work!?!?!
I have wrighten the exact code and put them in the right In / Out.

 

dchartier

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• May 16, 2005

• #6

hello dariusch;

Have you called your FC (in OB1 for example)?
Hope this helps,
Daniel Chartier

 

Dariusch

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• May 16, 2005

• #7

Yes I have calld the blok.

The "Toggle" only flickers, as if there is no "FP". But I have used the exact same code as that from Ken.

Dariusch

Edit//

Sorry not exact, I have not used the Inhibit, but as Ken said it was not nessasry.

 

SimonGoldsworthy

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• May 16, 2005

• #8

"oneshot" should be an in/out variable that is either a static variable in a function block, a bit in a db or an M flag bit.
Same applies to "Toggle" but this could be a Q output as well.

 

Dariusch

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• May 16, 2005

• #9

So you have to use a FB instead of a FC??

 

SimonGoldsworthy

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• May 16, 2005

• #10

No, oneshot must be in/out as this variable is written to as part of the FP instruction - use an M flag to prove it works.

 

DesertDog

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• May 16, 2005

• #11

With Siemens S7 I have actually had sucess with a simple function block.

  InOut              InOut

---| |------|NOT|-----( )

Where InOut is a local input/output variable.

It is called like this:

                      FC??

 Button   Bit      ---------

---| |----|P]------|  Tog  |

                   |       |

              InOut|       |

                   ---------

 

Ken M

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• May 16, 2005

• #12

Damn it - you turn you're head away for 5 minutes and there's a whole thread grown in front of you.

Simon's quite correct - in the original link I'd said ONESHOT should be an INPUT whereas it should be an IN_OUT. No-one corrected me then, and I'd just copied the link across. It wasn't that I meant to perpetuate my 'solution' - just to indicate that the topic had been touched on at least once before. Thanks, Simon.

regards

Ken

 

SimonGoldsworthy

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• May 16, 2005

• #13

Shouldn't "Toggle" be an in_out as well? Your FC uses the state of toggle to invert it with the x instruction. In an FC, "toggle" will be random if you use an output before it has been written to.

 

Ken M

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• May 17, 2005

• #14

Grrrnnnngghh!! (I think that's how it's spelled!)

I've just had a look in my library and, yes, sure enough, there are two IN_OUTs in my actual working version.
Apologies all round for pointing to this old thread which contained the original errors. I can only offer the excuse that it was errors brought about by typing enthusiasm rather than total ignorance. 'Ignorance' I'll accept, but not 'total' - there must be something I know. And hopefully, whatever it is, will be correct.

Regards

Ken

 

Dariusch

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• May 18, 2005

• #15

Just to understand how the FF works using the FC, why is it that it will work when using the "IN-OUT", but not when using the "TEMP"????

Could I have an explanation please??

Thank you

Dariusch