[Coco] MC6847 External Character ROM

[Juan Castro]

If that's the case, there must be some data line shenanigans similar to
those that make the block-graphics appear.


Juan Castro
Enviado do meu Olivetti Programma 101

On Mon, Jan 19, 2015 at 6:19 PM, Zippster <zippster278 at gmail.com> wrote:

> I was just about to comment on that.  The MC6847 set is 128 characters
> whether internal or external as far as I can tell.  In the video Juan
> linked
> I would guess the computer is switching into another rom bank for
> chars 128-255.
>
> - Ed
>
> > On Jan 19, 2015, at 2:09 PM, John W. Linville <linville at tuxdriver.com>
> wrote:
> >
> > On Tue, Jan 20, 2015 at 06:06:49AM +1000, Nick Marentes wrote:
> >> On 20/01/2015 5:52 AM, John W. Linville wrote:
> >>> You'll be limited to one of two 2-color options with these "graphics",
> >>> of course.  It could still be interesting, but it looses some luster
> >>> when you have to choose between light green & dark green or light
> >>> orange and dark orange... ;-)
> >>>
> >>> John
> >>
> >> That's for characters up to 128. Can the characters 128 to 255 (8 colors
> >> block graphics) also not be reprogrammed?
> >
> > The colors don't come from the ROM data.  The high bit of the data
> > in the RAM is fed back into the VDG to select the semi-graphics mode,
> > so the color and the encodings are all internal to the VDG.
> >
> >> Even so, hires graphics, even only light and dark green, would make VDG
> text
> >> displays so much nicer... and it only eats 512 bytes!
> >
> > It could be cool, yes.  Just not as cool as one might think at first. :-)
> >
> > John
> > --
> > John W. Linville              Someday the world will need a hero, and you
> > linville at tuxdriver.com                        might be all we have.  Be
> ready.
> >
> > --
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