DTR mask value

I currently trying to figure out what a petiular DTR instuction is doing in a RSlogix 5000 program. The instruction is using a tag value and then applying a mask. The question that I have is that the mask value in displayed as a negative one! If anyone out there has any insight into what a negative one mask accomplishes, please enlighten me!

The mask should be viewed in binary or hex representation for better readability

The DTR instruction is a weird one in that it is an input instruction that also writes to the reference value.

It is used to generate a true condition once each time the reference value does not match the source value.

It uses the mask to determine which bits to compare and which ones to ignore. The 1's are bits to be compared, and the 0's are bits to be ignored.

So each time the DTR is scanned, it will compare the source to the reference using the mask, and if there is a difference, it will allow the flow of logic to the next instruction, and write the source to the reference, also using the mask so as not to disturb the bits you want to ignore.

Paul

Thanks for the response, but my mask value(not the reference) is displayed as a -1. If I hover the mouse over the mask value, it displays "value:1"?? I didn't know if this "-1" manipulates the mask in some other way.

Convert decimal -1 to binary and what do you get?

Thanks for clearing things up!