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

[RETRO Innovations]

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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