Jeff,

I think you're right, it is a simple problem.

With PBP's ON INTERRUPT statement. The interrupt can only be serviced In-between PBP lines. So the "PAUSE 1" will limit the actual service time to an even interval of 1ms.

Just lose the PAUSE statement, and you should be a lot closer to what you wanted.

Personaly, I don't like ON INTERRUPT. ASM interrupts are much more accurate.

HTH,
    Darrel