They didn't use ladder logic in 5TI's? What was it I learned ladder logic on all these years ago then? You could switch between ladder and symbolic code. It all depended on what you were using to program it. The handheld programmer had symbolic code only, but the VPU200 used both ladder and symbolic.
You're absolutely right about re-writing the code however. The 5TI had a very limited instruction set so there shouldn't be anything really tricky in the programme. Basic Boolean logic, plus timers and counters. Add a couple of jump and master control relay commands and that's it. No arithmetic, no compares, no register handling, no indirect addressing (phew!). How on Earth did we ever control anything in those days!?
Regards
Ken