[Coco] CoCo 3's CoCo 1/2 mode

[Arthur Flexser]

Yes, shouldn't affect bank switching.

Art

On Mon, Aug 23, 2021 at 11:30 AM M. David Johnson <mdj at bds-soft.com> wrote:

> I see. So then the bit only affects the graphics, not the memory
> management,
> i.e. setting it doesn't limit the bank switching capability?
>
> --
> M. David Johnson
> mdj at bds-soft.com
>
>
>
> -----Original Message-----
> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Arthur
> Flexser
> Sent: Sunday, August 22, 2021 11:15 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] CoCo 3's CoCo 1/2 mode
>
> I found this at http://www.roust-it.dk/coco/Lomont_CoCoHardware_2.pdf
> -----------
> To use CoCo 3 graphics, the COCO bit must be set to zero. When using CoCo
> 1/2 resolutions, the bit is set to 1. RSDOS typically sets the INIT0
> register [$FF90] to 196 in CoCo 2 resolutions and 68 when using CoCo 3
> graphics modes.
> -----------
>
> So, it would seem that Bit 7 of $FF90 (the "COCO bit") is just something
> that has to be set appropriately by the user, or by the Basic ROM graphics
> routines, depending on whether the CoCo 3 or the CoCo 1/2 graphics modes
> are being employed.  It's not a general compatibility switch.  At startup,
> the CoCo 3 defaults to CoCo 1/2 graphics resolution, so $FF90 bit 7 starts
> out set to 1.
>
> Art
>
> On Sun, Aug 22, 2021 at 11:38 PM M. David Johnson <mdj at bds-soft.com>
> wrote:
>
> > I read that when Bit 7 of &HFF90 (cf.
> > http://www.cococommunity.net/socks-gime-register-reference/ ) is set,
> the
> > CoCo 3 is then in CoCo 1/2 mode.
> >
> >
> >
> > I don't have a physical CoCo 3 to check that on (I only have a CoCo 2).
> >
> >
> >
> > But in VCC 2.1.0d I notice that, immediately on startup, &HFF90 contains
> > &HCC (1100 1100 binary).
> >
> >
> >
> > So it's already in CoCo 1/2 mode? Am I missing something?
> >
> >
> >
> > --
> >
> > M. David Johnson
> >
> > mdj at bds-soft.com
> >
> >
> >
> >
> >
> >
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> > Coco at maltedmedia.com
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> >
>
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