trebor@biar.UUCP (Robert J Woodhead) (08/06/89)
I need to know, to as many significant digits as possible, the exact frame rates of the Mac II "Tickcount" variable (60.15 hz according to IM-V) and NTSC video. I have to passively sync some displays to freerunning video over a 30 minute period to within a couple of ticks, so I need to know the exacto numbers. Many thanks in advance. -- (^;-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-;^) Robert J Woodhead, Biar Games, Inc. !uunet!biar!trebor | trebor@biar.UUCP ``I can read your mind - right now, you're thinking I'm full of it...''
poynton@vector.Sun.COM (Charles A. Poynton) (08/09/89)
In article <812@biar.UUCP> trebor@biar.UUCP (Robert J Woodhead) writes: > I need to know, to as many significant digits as possible, the exact frame > rates of the Mac II "Tickcount" variable (60.15 hz according to IM-V) and > NTSC video. NTSC video frame rate is exactly 30/1.001 Hz, or roughly 29.97 Hz. Mac/Plus/SE displays have a dot clock of 15.6672 MHz; divide by 704 to get horizontal line rate (512 clocks have visible pixels), and divide by 370 to get vertical (342 of these lines are visible). Hence, Mac/Plus/SE frame rate is 15667200/704/512, or roughly 60.15 Hz. I suspect (but do not know for sure) that "Tickcount" corresponds to this value. Nuts to oddball frame rates. C. ----- Charles A. Poynton Sun Microsystems Inc. <poynton@sun.com> 2550 Garcia Avenue, MS 8-04 415-336-7846 Mountain View, CA 94043 "Japan has no laws against damage to its flag, but it has strict laws forbidding the burning of foreign flags lest this give offense to the country in question." -- The Economist, July 1, 1989, p. 19. -----