[Coco] Re: [Color Computer] Re: Adapter from Coo3 to SVGA

Torsten Dittel Torsten at Dittel.info
Tue Apr 5 03:18:58 EDT 2005

> Both the coco3 and the
> converter could syncronize to the vertical sync signal using it as
> the I2C clock.

Good idea. Hadn't thought in the clock.

> The PIA line could do full duplex by programming
> the PIA bit 3 in the register at &HFF22 for input or output on the fly
> as needed for the data signal.

Err... I guess its still half duplex that way (one direction at a time).
But of course it's bidirectional.
> Good ideas
> abound and flow freely for anyone to use.

Yes, it's free, a "public domain" idea! :-)

> The only
> problem I can see is that I wont be able to use the "standard"
> monitor cable people may already have (and you can get from
> cloud nine).   Not enough pins.  Cable has 6 pins and we
> need 7 unless someone knows how I could multiplex the PIA
> signal with one of the RGB signals.

I don't understand that. Isn't your adapter connecting to the CoCo's RGB
port and a standard VGA monitor is connecting to a d-sub15 type
connector on your adaptor?

>      The display is there after power up when you hit the reset button
>  on the coverter but it does not give a readable display, just a green "blob".
> Programming is necessary  because the default values
> for the registers in the video chips aren't compatible with
> the coco3's video output.

Strange. What kind of video signal is it expecting? What's not standard
of the CoCo's video signal? Which parameters of the AL250 are you
changing to make it readable? Could it be that beast is starting up in
component video mode and you have to change to RGB mode? I thought this
could be controlled by the pins of the AL250 and not just by software...


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