PLC Jobs
You need to create a 'PLC Job' area pointer. This is done from the system menu on Protool v5 and from the project tree on V6.
Give it an address (VW10 for instance) and it will allocate VW10, 12, 14, and 16.
To select a screen uses PLC Job 51.
In the PLC program, move 51 to VW10 and the screen number you want into VW12. (This job needs no more parameters)
Paul