NMI is edge triggered, IRQ is level triggered. If IRQ stays low then it will fire again when you RTI out of the interrupt handler. NMI has no mask, so it only fires when it transitions from high to low & there is nothing to stop another NMI from being triggered while the handler is still running. In fact it might be why it's looking for the keyboard scan, if the computer is scanning the keyboard then you know that the NMI handler has finished. On 03/10/2022 17:02, Jim Brain wrote: > I stand corrected, though I thought NMI was level triggered, while IRQ > was edge triggered. >Received on 2022-10-05 19:00:05
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