Any idea how this works - Indirect Addressing (Rockwell)

Hi I came across this instruction with this kind of addressing. Not sure how it works.

It's addressed as U.PO.B[U.Phase AND 255]

I'm trying to understand the [U.Phase AND 255] part.

I assume 'Phase AND 255' is not a tag. 'Phase' is a DINT and what does the and 255 mean??

What can I expect from this kind of addressing?

Thanks for your help. Pic attached.

antsrealm said:

'Phase' is a DINT and what does the and 255 mean??

Click to expand...

It's masking the low 8 bits in Phase (bitwise operation). So the final index is a number between 0 and 255.