[Coco] CocoFlash Updates

Darren A mechacoco at gmail.com
Sun Sep 18 16:01:20 EDT 2016

On Sun, Sep 18, 2016 at 5:03 AM, Gene Heskett wrote:

> I have lamented for at least 25 years because someone hasn't made a one
> chip addin board for the coco itself, restricting the address space used
> by the PIA's to the 4 byte wide access they need, which would free up 7,
> 4 byte wide addresses from $FF04-FF1F, and 7 more 4 byte wide blocks
> from $FF24-FF3F. Thats 14 more 4 byte wide devices we could address in
> those two spaces.

If a device wants to use the ghosted PIA addresses it can do so without any
need to modify the CoCo. Asserting the SLENB* pin on the cartridge port
disables the internal '138.

Unfortunately, the CoCo ROMs do use the ghosted addresses from FF1C-FF1F
during initialization, so that area should probably be avoided.
Additionally, if you want to be compatible with the Dragon, avoid using
FF04-FF07 as that range is used for the internal 6551 ACIA on the Dragon 64.

One thing I don't know is if the CoCo 3 GIME responds to any of the ghosted
addresses of FF22 for its shadowing of the old 6847 VDG control lines.

- Darren

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