Re: IIgs Double HIRES

["Marc S. Ressl" <mressl@gmail.com>]

On 12 feb, 20:05, Vladimir Ivanov <vlad...@XXXyahooXXX.com> wrote:
> On Sun, 12 Feb 2012, Charlie wrote:
> > On 2/12/2012 5:00 PM, Daniel Kruszyna wrote:
> >> Hello All,
>
> >> Has anyone documented the method that the IIgs uses to determine
> >> color in double hires mode? A search of the archives brings up
> >> some discussion, but not any findings...
>
> >> -- Daniel
>
> > The Apple IIgs Hardware Reference gives a small amount of information less
> > than a page and half including the usual table for figuring the color
> > pattern.
>
> The Hardware Reference claims 4-bit sliding window.
>
> There's also a bit in a register controlling B&W or color mode for Double
> Hires.
>
> > Having said this I would like to hear of something better myself as I
> > have struggled to understand the double hires mode.
>
> What exactly is troubling you?

Btw, I have a question that has been bothering me for quite some
time... what is the pixel clock for IIGS Super HIRES?

I understand that the pixel clock for HIRES and DHIRES is the famous
14.31818 MHz, and this gives you 560 pixels. As Super HIRES has 640
pixels, is the pixel clock the same (thus video shows with more
width), or is it stretched so 560 DHIRES pixels look like 640 SHIRES
pixels? What about the horizontal count, does it still go 0, 0x40,
0x40, ..., 0x7f as in the Apple II modes? And does visible video go
from 0x58 to 0x7f?

With the best wishes,

Marc.-

pd. guess why I'm asking these questions ;-)