[Coco] Last video I promise... :)

[Mark McDougall]

On 12/11/2014 11:02 PM, Luis Antoniosi (CoCoDemus) wrote:

> I needed a framebuffer because I couldn't make it to work without it. The
> GIME clock gets out of the sync with the VGA timing and I ended up having a
> rolling screen.
>
> The pixel clocks are not mutiple. While the GIME pixel clock is 14.318Mhz,
> the VGA pixel clock is 25.175Mhz

You can clock the VGA off 2x your GIME pixel clock, you don't have to be 
absolutely perfect on the 'standard' VGA timing, and even less so on CRT's. 
The monitor should be able to handle it; I've certainly not had any problems 
simply doubling the 'composite' clock.

> My converter needs a pixel perfect representation of the screen in order to
> reconstruct the artifact modes.

Surely you just need a line buffer to do that? Or do adjacent lines affect 
one-another for the artifact mode?

> Having a framebuffer in the middle gives me freedom to each component to
> work at their own speeds. Also, this solves the problem to convert from
> 50Hz to VGA 60Hz. I have a french coco2 peritel that does RGB SCART in 50Hz
> and a MSX computer that can operate in 50Hz NTSC.

OK, this I concur. I didn't factor in PAL video modes, despite being 
Australian! Doh! ;)

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"