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Home » Eclipse Projects » 4DIAC - Framework for Distributed Industrial Automation and Control » Comparing negative values(IEC61131-3 Equals block)
Comparing negative values [message #1821470] Thu, 13 February 2020 13:16 Go to next message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
Junior Member
Hello.

Can somebody give me a hint on how to check negative values to see if they are equal?

In my current application I have used an EQ block from the iec library. It works fine for positive values, but I soon realised that this is not true for negative values.

Casting the value to a dword does also not help as seen in the screenshot.

Is this behaviour expected and what would my alternative be?

Thank you in advance!

[Updated on: Thu, 13 February 2020 15:03]

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Re: Comparing negative values [message #1821477 is a reply to message #1821470] Thu, 13 February 2020 14:10 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
Messages: 96
Registered: March 2016
Member
Hi,

based on this very small snippet and the values I can see there, I would guess you are not using signed data types. How are your EQ ins typed (e.g., what are they connected with)

Best regards,
Martin
Re: Comparing negative values [message #1821484 is a reply to message #1821477] Thu, 13 February 2020 14:54 Go to previous messageGo to next message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
Junior Member
Hello,

Originally the values were INTs converted to DWORDs, so I tried changing the values to INT when I realised they are not the same size. This is probably converted to DINT I cannot tell exactly as I have tried out some things in the meantime, but it does not work either.

One is connected to the input data of my custom FB and the other is the read value from a ID block.
Re: Comparing negative values [message #1821485 is a reply to message #1821484] Thu, 13 February 2020 14:59 Go to previous messageGo to next message
Alois Zoitl is currently offline Alois ZoitlFriend
Messages: 1039
Registered: January 2014
Senior Member
ID delivers its values as DWORD. If you would like to have them in a signed format, or the value read is signed then you need a DWORD2DINT FB. Then the output should be signed. Please note that both datatypes connected to the EQ have to be of same type.
Re: Comparing negative values [message #1821486 is a reply to message #1821485] Thu, 13 February 2020 15:07 Go to previous messageGo to next message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
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Hello Alois,

I have provided a screenshot of my current test application. I hope this helps.
Re: Comparing negative values [message #1821487 is a reply to message #1821486] Thu, 13 February 2020 15:10 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
Messages: 96
Registered: March 2016
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Hi Mario,

there is no screenshot attached
Re: Comparing negative values [message #1821489 is a reply to message #1821487] Thu, 13 February 2020 15:15 Go to previous messageGo to next message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
Junior Member
The screenshot is attached to the original post. Sorry for the confusion
Re: Comparing negative values [message #1821490 is a reply to message #1821489] Thu, 13 February 2020 15:16 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
Messages: 96
Registered: March 2016
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Oh ok, and it does not work this way?
Re: Comparing negative values [message #1821492 is a reply to message #1821490] Thu, 13 February 2020 15:20 Go to previous messageGo to next message
Mario Krizic is currently offline Mario KrizicFriend
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Sadly it does not for negative values. Can anybody else confirm such behavior?
Re: Comparing negative values [message #1821493 is a reply to message #1821490] Thu, 13 February 2020 15:20 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
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Is it on purpose, that the FBs names are F_DWORD_TO_INT (signed), but are of type F_DWORD_TO_UDINT (unsigned)?
Re: Comparing negative values [message #1821494 is a reply to message #1821493] Thu, 13 February 2020 15:21 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
Messages: 96
Registered: March 2016
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Ok, just seeing your post now. You are using the wrong FBs. You need F_DWORD_TO_DINT without the U
Re: Comparing negative values [message #1821495 is a reply to message #1821494] Thu, 13 February 2020 15:32 Go to previous messageGo to next message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
Junior Member
I have changed the block types a lot, therefore the name does not match the type.

After changing the types I ran the program again and you can see that the EQ block outputs false only when comparing negative values. Thoughts?

[Updated on: Thu, 13 February 2020 15:32]

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Re: Comparing negative values [message #1821499 is a reply to message #1821495] Thu, 13 February 2020 16:06 Go to previous messageGo to next message
Martin Melik-Merkumians is currently offline Martin Melik-MerkumiansFriend
Messages: 96
Registered: March 2016
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Hmm,

seems like a bug. I will check this on my machine
Re: Comparing negative values [message #1821889 is a reply to message #1821499] Fri, 21 February 2020 15:52 Go to previous message
Mario Krizic is currently offline Mario KrizicFriend
Messages: 29
Registered: April 2019
Junior Member
If anybody has the same problem a quick workaround I found was converting the values to STRING as the EQ block seems to have no problem processing them. It seems inefficient, but it works until the bug is fixed.
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