[Coco] EEPROM replacement for 27C256

[John B]

Yup.  The ones I ordered were 90ns.  Putting the socket in the CoCo3
tonight.  Now if my darn TL886 would get here. :)

On Mon, Jun 29, 2015 at 2:04 PM, Dave Philipsen <dave at davebiz.com> wrote:

> Yes, I think that's right. Another benefit of the 29c256 is that it
> appears to be available with faster access times.
>
> Dave Philipsen
>
> > On Jun 29, 2015, at 7:19 AM, John B <trymyz at gmail.com> wrote:
> >
> > 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?
> >>>>> --
> >>>>> Coco mailing list
> >>>>> Coco at maltedmedia.com
> >>>>> https://pairlist5.pair.net/mailman/listinfo/coco
> >>>> Cheers, Gene Heskett
> >>
> >>
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> >
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