9 times out of 10, my program awakes fine (IOC interrupt related), but....

[HankMcSpank]

Golden rule for interrupts.
Once in get out as quick as possible.
My guess is GOSUB a time or two will violate the golden rule.

Yes, seeing the whole code could help

I no longer have Gosubs in my interrupt - I removed them.

The problem seems to be the Gosub in the main body of code - when I leave them in, the IOC interrupt routine or my program hangs once in every 8-10 switch presses.
(not sure which yet...when it hangs, the last debug line I see is that from inside in the interrupt routine!)

I'm presently trimming my bloaty program right down (most of it is just visual 'white noise' lol!)...once i've slimmed it down but can still replicate the problem I'm experiencing, then I'll post up the code....at least then you'll have a chance of picking through it!

Henrik - re the missing underscore - that was just a rough high level example of my approach - not my code (& it was *very* late UK time!)