[Coco] CoCo's TIMER and 60hz

Allen Huffman alsplace at pobox.com
Wed May 29 13:17:59 EDT 2019

> On May 29, 2019, at 12:14 PM, Bill Nobel <b_nobel at hotmail.com> wrote:
>  Roger and I ran a test last night with my logic analyzer on a real Coco3.  VSYNC on the particular machine I tested reported 59.7 Hz.  The Coco3 was never accurate on software time due to fact the IRQ line is shared with other devices besides VSYNC.  Yes they are queued but arn’t serviced accurately based on time.

Anything that masks interrupts can throw a timer using it off, of course — disk access, and I think even playing a tone masks IRQs (?) in BASIC.

My question at this point is trying to determine if Matchbox CoCo is just off, or if there would be similar drift between two different CoCo 3s running the same BASIC program.

		— Allen

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