[Coco] CoCo2 Strange Side Switches

[Rogelio Perea]

On Wed Dec 3 2014, John Goerzen wrote:

On that larger chip (MC6847P), it appears that both switches have a wire
> connected to one of its legs - the second down from the top on the right.
> It is a little hard to determine where the other wire on that chip is
> going,
> but I think it's the top on the right.
>
> Then there's that wire to the smaller chip, and it's connected to the
> top-right leg of it.
>
> Does this give any clues?
>

As Louis noted, the mod seems to be a way to have the video display
generator switch screen modes. On the CoCo 1/2 the VDG is set to follow ROM
setup code to the standard green screen on black border display, you can
POKE other modes like orange on black border (text remains black) and other
combinations but the CoCo will switch back sooner or later - the switches
were a way to hardwire the VDG to force it to remain on a given mode.

Tony DiStefano wrote of such mods for his Rainbow magazine "Turn Of The
Screw" column.

Connect the CoCo to a TV and power it up to different on/off combinations
on the switches,, see what happens to the display.


-- RP