Digital outputs located outside the process image !

Hello Tomy,

try to explain as simple as i can)

1) Perihierial area could be write/read ONLY by bytes or longer.

2) PQB cant be read, PIB cant be written (although QB and IB could)

3) From 1) and 2) first solution - use addresses inside process image area. You say thats impossible, ok let it be (but seems strange a little bit, please clarify why if you can).

4) From 1), 2) and 3) follows second solution: you need to store whole byte to output somewhere -DB or M area (#Current_output for ex.) and write it to PQB as byte. Then you can modify certain bits, read them etc. - in #Current_output.

Next - all your inputs are set in programm somewhere, so if you restart PLC your variable #Current_output will be syncronized with PQB always. If you cant restart PLC then you need to preset #Current_output with certain value - you can do it if you'll watch at DO module LEDs - after that you can modify your programm to work with #Current_output instead of PQB (by presetting #Current_output you can guarantee bumpless switchover to new programming blocks)