Copy data from SINT array to UDT

[RAndersson]

Hello!

I am completely new to PLCs, so I apologize in advance if this is a dumb question.

I have a device that sends out its data as a number of configurable data types, for example 4 SINTs, 1 DINTs and 6 SINTs. This arrives in the PLC as a SINT array of matching size. So, for example if the device is configured to send out 4 SINTs, 1 DINTs and 6 SINTs the data arrives in the PLC as a SINT array of length 4 + 1*4 + 6 = 14.

In addition, I have a User data type that my device can export that matches the data types, so for the example above: 4 SINTs, 1 DINTs and 6 SINTs.

What I want to do is to copy the content of the SINT array to a tag of type myUDT. To do so, I am trying to use (Which I am not sure is the correct way):

COP(myDevice:I.Data[0], testTag, 1)

or

COP(myDevice:I.Data[0], testTag.firstElement, 14)

This works for the first 4 SINTs, but the DINT data is not correct. In addition, the data in the 6 SINTs following the DINT is offset 3 positions backwards (So data data in the SINT array position 13 (The last one) is copied to the fourth last SINT in testTag instead of the last)

As a test, I tried to copy 4 bytes in the SINT array to the DINT alone, and this works:

COP(myDevice:I.Data[4], myDINT, 1)

Is there a way to copy the content of the SINT array to the UDT in this way?

 

[RAndersson]

I might have figured something out: If the DINTs are placed on positions evenly divided by 4, then it works, else it does not. For example, a structure like:

3 SINTs, 1 DINT, 4 SINT

Does not work, while

4 SINTs, 1 DINT, 4 SINT

Works (Using COP()).

 

[bb76]

Hello!

So, for example if the device is configured to send out 4 SINTs, 1 DINTs and 6 SINTs the data arrives in the PLC as a SINT array of length 4 + 1*4 + 6 = 14.

A DINT is 2 INTs (or 4 bytes/32 bits) so you would have an array length of 12

 

[plvlce]

A DINT is 2 INTs (or 4 bytes/32 bits) so you would have an array length of 12

The array unit is SINT, which is half an INT or 1 byte. A DINT is 4 SINT.

 

[drbitboy]

https://en.wikipedia.org/wiki/Data_structure_alignment

 

[RAndersson]

https://en.wikipedia.org/wiki/Data_structure_alignment

Thank you.

This also explains why a UDT with:

3 SINT, 1 DINT, 1 SINT

is 12 bytes, while a UDT with:

1 DINT, 4 SINT

is 8 bytes.

I will enforce that data types of size 4 (DINT, REAL etc) can only be placed on indexes that are multiples of 4 and data types of size 2 (INT etc) on multiples of 2 in the device.