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

[Robert Gault]

Of course one could always assume that VCC is working correctly regards the content of $FF90 and read the contents when in different screen modes, text and graphics.
You should be able to find the CoCo3 service manual in the colorcomputerarchive.com under documents which will list what the bits do. However, the fun of having the hardware or emulator is writing programs to see what you can do with the unit. 😄
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  On Mon, Aug 23, 2021 at 12:15 PM, Arthur Flexser<flexser at fiu.edu> wrote:   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
> > https://pairlist5.pair.net/mailman/listinfo/coco
> >
>
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