Hans,

Exactly right. Most of the time, in my applications, the external interrupt is from a keypad decoder which is slow. I agree that the ISRs have to be short and must be well thought out and speedy.

BTW I started out programming on the 6502 which had only two interrupts NMI and IRQ, so I got into the habit of disabling the IRQ in the ISR because it could be interrupted during the ISR in hardware.

Regards,

Jacob