Hallo William, > I checked my files and I don't have 970150, That's nad news. Any one else? > but at some time I coppied the register values. Okay, now we need the other 2030 Bytes ... ;-) > This was for a 9" PET which had the system board > replaced. So the old system board without CRTC was replaced with a board with CRTC. > The ROM was an EPROM, obviously with the CRTC programming > patched. Yes, it think too, this 970150-07 must be near to 901474-03 with changed crtc registers. But it's possible, they changed anything else, too. > This could also be used with an adapter to drive external > monitors. The 50Hz PAL is probably for an external monitor, otherwise > there is no reason to make it PAL compatible. In which case, monitor > size doesn't matter. Isn't it? This 901474-04_ can be for an european system board replacement with 50 Hz. This must be working with a 9" crt. The changes about 970150-07 and 901774-04_ must be the 50 / 60 Hz difference. So 901774-04_ looks to 970150-07 as 901774-04 to 901774-03! My first idea was too, the 901774-04_ was used to drive an external pal montior. And yes, i remember we upgraded a thin 40 system with a 80 columns video card and replace the 9" crt with a 12" zenith monitor. So this monitor need pal sync. So we need an patched editor rom with pal frequency, too. But i don't remember anything about the source of this rom. > The internal monitors use ramp generators for the horizontal sync. As > long as the supplied sync rate is close, the monitor locks on. The > registers on the CRTC are only one byte in length, limiting the > accuracy of the resultant sync rate. The values chosen by the > programmers provided the desired appearance on the screen, knowing > they could be a little off and still have it work. Yes, that's true. So the accurated value isn't needed. But the high voltage is defined over the horizontal frequency. Martin Message was sent through the cbm-hackers mailing listReceived on 2015-05-05 20:00:06
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