Missing Higher Bits in OPC Tag Data from PLC

Updated Nov 22, 2018

Reported In


  • OPC Servers

Issue Details

I am using NI OPC Server to grab OPC data tags from my PLC. I have configured the tag data type as Short (16-bit) in NI OPC Server but all the tag data I receive are capped at 255 (8-bit). Why is this happening?


First of all, please check the data type of the outputĀ registers on your PLC. If the register data types are all correct, then it is probably due to the output mechanism of your PLC.
Some PLCs only output the lower 8 bits of the data even though the registers are set as a 16-bit data type (e.g. Word).
You may need to split your data on your PLC for output if you want the full bits.