Changing Pointer Value in AB SLC SQO Function

I am building a traffic light simulator that I will be using to demonstrate PLC's at my sons' 5th grade elementary school as part of their STEM program.

I have created a program using a sequencer to step through signal & walk/don't walk phases for both directions. Now I would like to add left-turn lights but I want their operation to be based on positive detection of a vehicle in the left turn lane prior to the signal servicing that direction of traffic.

My thought was to add a green & yellow left-turn phase to each direction's SQO data file that would start after expiration of the 4-way red phase BUT ONLY IF A VEHICLE IS DETECTED. If I determine that none is present, I was thinking that I could change the value of the SQO's pointer directly to make it skip the LHT phase. Does this sound correct? Also, if I do this, will the SQO only change its output following another false-to-true transition? If that is the case, then I would guess that the pointer would need to be set to a value of (n-1) where n is the desired state.

Thanks in advance!
Jimmy

You are absolutely on the right track, manipulate the .POS register of the SQO control structure as you see fit.

Program your SQO source bit-file for all eventualities, and simply skip past the left-turn sections when a vehicle is not present in the respective lane.

I believe the data is copied once only, following a false-to-true transition of the instruction, but I can test this and post back.