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Comparing negative values [message #1821470]

Thu, 13 February 2020 08:16

Eclipse User

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!

Attachment: EQ_NegativeVal.PNG
(Size: 6.52KB, Downloaded 70 times)
Attachment: AbsPosTest.PNG
(Size: 172.82KB, Downloaded 82 times)

[Updated on: Thu, 13 February 2020 10:03] by Moderator

Re: Comparing negative values [message #1821477 is a reply to message #1821470]

Thu, 13 February 2020 09:10

Eclipse User

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 09:54

Eclipse User

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 09:59

Eclipse User

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 10:07

Eclipse User

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 10:10

Eclipse User

Hi Mario,

there is no screenshot attached

Re: Comparing negative values [message #1821489 is a reply to message #1821487]

Thu, 13 February 2020 10:15

Eclipse User

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 10:16

Eclipse User

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 10:20

Eclipse User

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 10:20

Eclipse User

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 10:21

Eclipse User

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 10:32

Eclipse User

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?

Attachment: AbsPosTestMonitored.PNG
(Size: 203.07KB, Downloaded 79 times)
Attachment: AbsPosTestMonitoredPositive.PNG
(Size: 199.29KB, Downloaded 82 times)

[Updated on: Thu, 13 February 2020 10:32] by Moderator

Re: Comparing negative values [message #1821499 is a reply to message #1821495]

Thu, 13 February 2020 11:06

Eclipse User

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 10:52

Eclipse User

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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