[Coco] EEPROM replacement for 27C256

[John B]

Great information.  As for the EEPROM vs Flash, my understanding is the
CoCo3 will still read the information the same way, the main difference is
how its programmed.  I will be using TL866 so I should be ok.  Let me know
if I am off base.

John

On Sun, Jun 28, 2015 at 7:33 PM, Dave Philipsen <dave at davebiz.com> wrote:

> Good point.  A couple of reasons for uniformity might be for ease of
> programming with standardized programmers and for certain internal
> page/block write operations operations that may require certain address
> lines to be assigned correctly.  Also, the 28C256 polls the D7 line to
> verify when a programming operation has finished although that could be
> taken care of through software.
>
> As far as the 29C256 is concerned, according to the strictest sense of
> nomencalture  it is not an EEPROM but a FLASH.  I don't think you can write
> single bytes with the 29C256 like you can with the 28C256.  But the 29C256
> might be just the ticket for you if you understand the way it works.
>
> Dave Philipsen
>
> On 6/28/2015 12:55 PM, Gene Heskett wrote:
>
>> Another piece of trivia folks.
>>
>> As long as the data buss is the same width AND on the same series of
>> pins, it doesn't matter one bit if data pin d0 is connected to the data
>> line on the board named d0. Ditto for d1-d7 (or d15 for 16 bit wide
>> chips) Because any sucn accidental or on purpose scrambling simplifies
>> the board layout, scrambling of the data written, it will be unscrambled
>> by the same "re-arrangement" on the subsequent read.  You will get back
>> the same data you wrote in any event.
>>
>> Exactly the same situation exists for the address lines, the operative
>> again is that the same group of pins are being used.  The a0 thru a15
>> (or a23, a31 in the case of wider chips) can be fed to the chip in any
>> sequence.
>>
>> As long as those conditions are met, it will work as expected.
>>
>> I can think of a flash eprom that would need exact matching because they
>> often have to erase and rewrite a whole 4k block to change one bit.  The
>> cocosdc might, probably is subject to that exception, but Darren can
>> correct me.
>>
>>  On Sun, Jun 28, 2015 at 12:17 AM, Dave Philipsen <dave at davebiz.com>
>>>
>> wrote:
>>
>>> There is a 28C256 that is as probably as close as you'll get in
>>>> terms of pinout.  It won't be an exact drop-in replacement, though,
>>>> as the A14 pin changes position and you'll have to come up with a
>>>> write enable as, obviously, the 27C256 which is a primarily
>>>> read-only device does not have. I have a 28C256 floating around here
>>>> somewhere that I used in a custom circuit I built one time but I've
>>>> never tried to wire it up to a CoCo3. One thing for sure, you'd have
>>>> to make sure that any changes written to the EEPROM contain no
>>>> undesirable code that could cause the CoCo to become unbootable.
>>>> Otherwise you'd have to pull the 28C256 and re-program it out of
>>>> circuit.
>>>>
>>>> Dave Philipsen
>>>>
>>>> On 6/25/2015 2:43 PM, John B wrote:
>>>>
>>>>> Does anyone know of a suitable EEPROM replacement for the 27C256
>>>>> found in the CoCo3?
>>>>>
>>>> --
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>>>> Coco at maltedmedia.com
>>>> https://pairlist5.pair.net/mailman/listinfo/coco
>>>>
>>> Cheers, Gene Heskett
>>
>
>
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