HI
I have a question in regards to control and notify words of a omron HMI (NT11S - NT31) and that is when a screen is changed by pc then the bit or the combination of bits in control word becomes one (1). Does it mean that the same change happens to notify word. Thanks Mike

Hi, control area is when you want PLC send to HMI wich screen number to switch to. If my memory is good it is the first word of control area.
Notify area is when you want PLC to read from HMI wich screen is actually displayed. Again, if my memory is good, it is the first word of notify area.

For better explanation see section 2-2 of this manual:

http://forums.mrplc.com/index.php?autocom=downloads&showfile=383

There are 2 different PT Notify / PT Control schemes, 1 older, 1 newer.
In the old scheme (NT20M, NT20S, NT30, NT630), the first word of the Control area was where you write data to command a screen change from the PLC, and the first word of the Notify area showed the current screen, regardless of how you got to that screen.

In the new scheme ( NT21, NT31, NT631), the first word of the PT Control area was where you write data to command a screen change, and also were the current screen is shown.

I would need to double check the manual, but I think the NT11S follows the 'old' method.

Shown below is the 'new' method.

Click to view attachment