The Sinclair QL Forum

Hi all,

Is the EXTINT level or edge triggered ? It's documented as being active low, however is it triggered constantly whilst held low, or only triggered on a high to low transition ?

Cheers.

Phill.

EXTINT into ZX8302 is level triggered, ie. it will cause interrupts until cleared (to high level).

There was an early problem with QIMI and soft resets that didn't also do a hardware reset. The computer could lock up if you moved the mouse before PTR_GEN was reloaded.

The fact that this happened despite the EXTINT bit in ZX8302 interrupt register being cleared at the end of every level 2 vector call means that a high/low transition on EXTINT isn't needed to re-establish interrupt.

It's level triggered, and it's down to the interrupting device to provide some sort of interrupt acknowledge method which then returns the EXTINT line back high - such as reading or writing some hardware register etc.