Hi Tom,

The problem might be caused by gosub, which might take too much time, because PBP uses very latency interrupt implementation, and it never jumps into interrupt subroutinue within gosub. Please read Section 9.2 "Interrupt in Basic" in PBP manual. If you use goto instead of gosub, the problem may be fixed. That is,

change

gosub AAA
...

AAA:
...
return

into

goto BBB
CCC:
...

BBB:
...
goto CCC

If the above does not work, you have no choice but using assembly interrupt.