Re: Timer interrupt frequency (50Hz vs 60 Hz)
Bruce Borer via Coco <coco-uNHYcr1XS/wmlAP/[email protected]>
| Newsgroups | gmane.comp.hardware.tandy.coco |
|---|---|
| Message-ID | <CAFoCBXxiJ9AXB0CCGcb3f8gq+3iK3WUq1MmRY15eyw9F8MV_fw@mail.gmail.com> |
From extended-basic-unravelled page A-11 address $FF98 bit 3 indicate the refresh rate 0 for NTSC, 1 for PAL. is this what you are looking for? 0769 FF98 BIT0 LPR0 LINES PER ROW (SEE TABLE BELOW) 0770 BIT1 LPR1 LINES PER ROW (SEE TABLE BELOW) 0771 BIT2 LPR2 LINES PER ROW (SEE TABLE BELOW) 0772 *BIT3 H50 1 = 50 Hz VERTICAL REFRESH* 0773 BIT4 MOCH 1 = MONOCHROME (ON COMPOSITE) 0774 BIT5 BPI 1 = BURST PHASE INVERTED 0775 BIT6 0776 BIT7 BP 0 = ALPHA, 1 = BIT PLANE Bruce P. Borer [email protected] On Thu, Mar 20, 2025 at 7:05 PM RETRO Innovations via Coco < [email protected]> 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 <[email protected]> > 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 > > -- > RETRO Innovations, Contemporary Gear for Classic Systems > www.go4retro.com > store.go4retro.com > > > -- > Coco mailing list > [email protected] > https://pairlist5.pair.net/mailman/listinfo/coco > -- Coco mailing list [email protected] https://pairlist5.pair.net/mailman/listinfo/coco