[Coco] EEPROM

[Patrick Ulland]

Been there.... some data for the fire. Not only does the CoCo not select 
ROMs during write cycle, the MPI doesn't enable ENBUS. For CoCoIOr, we 
have to assert SLENB to make writes work, after that MPI of course tries 
to write to all the slots at once. To allow multiple cards, we added a 
physical write lockout switch, will become a flipflop in the next design.

In other news, we chose the Atmel AT28c64B EEPROM. It's working with 
newer CoCos. We've found a couple CoCo1 D boards and a specific early 
CoCo2 motherboard  that won't boot from it directly, but will with the 
card in a Multipak. Note, bootup is just reads. Straight CTS, no control 
or timing malarkey. Haven't quite figured that one out yet.

good luck!

  -rick




On 6/28/2024 11:31 PM, Bruce Borer via Coco wrote:
> Be aware the CoCo does not chip select the ROMs for writing.
> I have made an adaptor to allow writing 4M Flash chips and to select
> which page is active.
> My CoCo3 is acting up so I have not fully tested my board.
> If anyone is east of Toronto that could help me test I would appreciate it.
> Bruce
>
> On Fri, Jun 28, 2024 at 10:55 PM dave--- via Coco<coco at maltedmedia.com> wrote:
>> Thanks, Dave. I was unaware of those chips. After looking at their data sheets it seems they may have continued to use the “27” designation because of their strong similarities to a standard EPROM. It appears that both of them are programmed like an EPROM and that they can be erased only as a whole chip which is also similar to an EPROM but done electrically instead of with UV.
>>
>>
>> -Dave Philipsen
>>
>>> On Jun 24, 2024, at 10:24 AM, David Ladd via Coco<coco at maltedmedia.com> wrote:
>>>
>>> On Sun, Jun 23, 2024 at 10:13 PM Dave Philipsen via Coco <
>>> coco at maltedmedia.com> wrote:
>>>
>>>> Dave,
>>>>
>>>> I think he is specifically looking for EEPROM. the 27 series is EPROM
>>>> and the 29 series is flash.
>>>>
>> --
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