Cognex barcode data comparison in PLC

I have installed a Cognex barcode scanner on a machine. I have a 1769-L18ER CompactLogix processor.

I have communication setup and working.

I have the 4 digits from my barcode scan coming into the PLC as SINT into:

COGNEX:I.ResultData[0] = 1
COGNEX:I.ResultData[1] = 0
COGNEX:I.ResultData[2] = 2
COGNEX:I.ResultData[3] = 5

So my barcode read is "1025" which is correct. The barcode is the current date. (Month and Year)

I want to compare this to two STRING files already in the PLC...

Print.ST16[30] = 10 (current month)
Print.ST16[31] = 25 (current date)

Im having trouble figuring out how to compare this data.. Basically I need to combine COGNEX:I.ResultData[0] and COGNEX:I.ResultData[1] to get my month and COGNEX:I.ResultData[2] and COGNEX:I.ResultData[3] to get my date, then compare each of those to the existing Print.ST16[30] and Print.ST16[31]

any help would be greatly appreciated. I hope i explained it well enough

You have to concatenate COGNEX:I.ResultData[0], COGNEX:I.ResultData[1],COGNEX:I.ResultData[2],COGNEX:I.ResultData[3] and convert the whole thing to an integer 1 "1025" in this case, then get month an day from wallclock and concatenate them to get another integer 2 "1025", then compare the two of them.

the data coming from my barcode scanner is in SINT format. Can i Concatenate two SINTs into a string?

widelto said:

You have to concatenate COGNEX:I.ResultData[0], COGNEX:I.ResultData[1],COGNEX:I.ResultData[2],COGNEX:I.ResultData[3] and convert the whole thing to an integer 1 "1025" in this case, then get month an day from wallclock and concatenate them to get another integer 2 "1025", then compare the two of them.

Click to expand...

I have to concatenate COGNEX:I.ResultData[0] and COGNEX:I.ResultData[1] together then concatenate COGNEX:I.ResultData[2] and COGNEX:I.ResultData[3] right?

then concatenate the results from the 1st one and the 2nd one together.

but the data from the barcode scanner is in SINT format. What type of data is the location they go into?

I think you will have to convert the SINTS to individual strings first, and then concat them together into one string.

dwoodlock said:

I think you will have to convert the SINTS to individual strings first, and then concat them together into one string.

Click to expand...

I used the COP instruction to copy the SINT to a STRING but the result is just showing a " symbol. Do i need to be online with the processor for this to show the actual data being moved? Im doing this at my desk right now.

You should be able to copy the 4 SINTs to a DINT, then do a DTOS to convert the DINT to String.

Edit just seen you are comparing to 2 strings, you can convert your compare value to 1 string and do the above or convert your 4 SINTs to 2 Strings and compare to the original 2 strings.

@Sean Teague:
I made program several years ago where I concat a lot of things please go to :
https://github.com/drbitboy/Logix_Zebra
And download it from there, the pdf is also at the same place.

I did a COP for the SINT to a DINT. Then a DTOS.... but i am not seeing a value in the destination. Do I need to be online with the processor to see this? as i am at my desk and offline right now.

Copy [0],[1],[2] and [3] at the same time to form a string "1025" ,
Or copy [0] and [1] at the same time to form "10" then convert it to int , then compare to month your get from wallclocktime
Use the same with [2] and [3]

widelto said:

Copy [0],[1],[2] and [3] at the same time to form a string "1025" ,
Or copy [0] and [1] at the same time to form "10" then convert it to int , then compare to month your get from wallclocktime
Use the same with [2] and [3]

Click to expand...

Could you explain in a little more detail how to do this?

I´ll try to do my best , see attached figure

Codigo_Barras means Barcode in spanish, that´s my mother language.
As you can se my code is composed from 14 sints (EAN14), but wait my code is numbered from [0] up to [13], I can copy (COP) just two items [0] and [1] or you can copy the whole thing, I mean 14 sints
Do you know how to do it. ??,

Yes you ned to be online with the processor to se the functions work or use the emulator if avaiable.

I did not see it, yes definitively you have to be online or thru emulation, otherwise It won´t work.

You cannot simply COP a SINT into the DATA of a String tag and expect the correct result -- despite the fact that Strings are made up of 'SINT' they are interpreted as ASCII, and the ASCII representation of a number is not the same as the actual value of that number.

For example, if in widelto's screenshot above you were to change the representation from 'ASCII' to 'Decimal', you would see that '1' is actually 49 for the first character of the string. If you copy from a SINT with a 1 in it into the SINT of a String, the resulting ASCII value will be a 'Start of Header' character, (shown as '$01') not a '1' character.

This is why a DTOS is used, to convert the value into the ASCII representation. You could technically add your own math to convert, but why bother when there's an instruction that does the work for you and is less likely to confuse anyone who looks at your code later?

Note that contrary to what the name might suggest you do not need to use an intermediate DINT, the DTOS instruction supports both SINT and INT input).

EDIT: See attached for an example. 'NullString' should be an empty string tag.