[Coco] Timer interrupt frequency (50Hz vs 60 Hz)

[Alex Evans]

Yes, you can interrupt (IRQ) on hsync on any coco.

On Thu, Mar 20, 2025, 19:05 RETRO Innovations via Coco <coco at maltedmedia.com>
wrote:

> On 3/20/2025 4:20 PM, Allen Huffman via Coco wrote:
> >> On Mar 20, 2025, at 4:17 PM, Juan Castro via Coco <coco at maltedmedia.com>
> wrote:
> >>
> >> The timer interrupt hits 60 timer per second in CoCos made in the
> Americas
> >> and a couple of other places, and 50 Hz in Europe and elsewhere. This
> means
> >> if I want to count seconds with BASIC's TIMER function, I need to be
> aware
> >> which kind of CoCo I have, 50Hz or 60Hz. Is there a way to find out
> which
> >> frequency I have by software?
> > Considering this was one of the questions apps would ask (like Nick
> Marentes’ games), I think not :(
> >
> >> I just thought of a horrid solution: count how many times a loop ran
> >> between two interrupts, and apply some tolerance. Of course, I'd have to
> >> set CPU frequency to baseline 0.89 MHz beforehand. Get typical values
> and
> >> apply some tolerance. Do I really need to do that?
> > That might indeed be the way to go. It would only take a 1/50th of a
> second, if you could time it that fast ;-)
> >
> >               — A
> >
> >
> >
> My VDG is rusty, but can you IRQ per scanline?  If so, can't you count
> the number of lines in a frame, or do the lines outside the screen not
> register?
>
> Jim
>
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