[Coco] EEPROM selection

[Bruce Borer]

Microchip makes the Flash SST39SF010A / SST39SF020A / SST39SF040 that
takes the 28 pin format and expands it to 32 pins.
It needs a simple adaptor board to use the Flash. The SST39SF040 gives
you 16 pages of 32K, the size of the CoCo3 ROM.  You will need
to determine how to select which 32K you want to use, either by
jumpers, switches or add logic to make it software selectable.

I am debugging a board that uses a micro to add additional features.
My CoCo3 currently has video problems which I am debugging
when I have time.  My board may be working but I need a display to test it.

The Micro adds:
- software selectable banks of 32 K
- allows you to write to the Flash even though the ROM select only
supports reads
-  the above is done in circuit. Note The CoCo needs to be running in
RAM when changing the Flash.

If you or anyone else is interested in the design, let me know. If you
are in the Toronto (GTA) area maybe you can help me test this board.

Bruce

On Sun, Jul 28, 2024 at 6:32 PM Patrick Ulland via Coco
<coco at maltedmedia.com> wrote:
>
> Warning, I am an old sysadmin. As such, I identify this as 'the XY
> problem'.
>
> Instead of asking about X (EEPROMs suitable for CoCo motherboard),
> you've already decided a RaspPi will be the solution and now need Y, the
> imaginary 3.3v writable, 5v readable EEPROM to implement the chosen
> solution.
>
> The result, X cannot be solved because there is no solution for Y.
>
> But Y is an added, artificial constraint. Forget assumptions and ask the
> real problem, how do I program a new ECB ROM with minimal external
> hardware. Somebody will have a practical answer to the original question
> that uses cheap chips and maybe a $30 programmer.
>
>
> -ricku
>
>
>
> On 7/28/2024 12:02 PM, dave--- via Coco wrote:
> > Since you asked for an EEPROM that could work at *either* 3.3 *or* 5V then the answer is yes. There is not likely an option for an EEPROM that works at both 3.3 *and* 5V though.
> >
> >
> > -Dave Philipsen
> >
> >> On Jul 26, 2024, at 6:15 PM, coco--- via Coco <coco at maltedmedia.com> wrote:
> >>
> >> All
> >>
> >> Is there an EEPROM that can work at either 3.3 or 5 V and can
> >> replace the Coco 3 motherboard ROM.
> >> I saw an article about how to use the GPIO of a raspberry pi at
> >>   https://www.instructables.com/Raspberry-Pi-Python-EEPROM-Programmer/
> >> I wondered if such a setup could read a coco ROM and write to a
> >> EEPROM chip suitable for a replacing the coco ROM and also
> >> which chip would you recommend for this purpose the chip used in
> >> the example is 4X the memory of a coco3 ROM.
> >>
> >> Charlie
> >>
> >> --
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> >> Coco at maltedmedia.com
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> >
>
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