On 26.09.2013 20:56, Kaz Kylheku wrote:
> On 26.09.2013 19:15, Kaz Kylheku wrote:
>>
>> I now have two Xicor X2864AD-25 EEPROM chips!
>
> Unfortunately, though these chips are pin compatible with the
> Toshiba TC5565AP static RAM, they have monstrously long write
> cycles that the MP-1's firmware won't deal with.
I understand now. The obvious solution is to make a chip which uses SRAM
as a fast cache, but internally flushes it to EEPROM at its own pace and
when the power goes out.
So that it can expose the same fast interface to the host system as the
battery-backed SRAM chip, and the host's firmware doesn't need to be
modified.
Well, turns out, this obvious hack exists! A company called ZMD made
chips exactly like this. An 100 uF external capacitor is required to
provide juice, when the main voltage goes out, for just enough time for
the volatile SRAM memory to be flushed down to the nonvolatile EEPROM
backing storage, all transparently by the chip, and nobody is the wiser.
This feature is called "AutoStore".
ZMD's nonvolatile business was acquired by Simtek in 2005. Story:
http://www.eetimes.com/document.asp?doc_id=1158054
Simtek was in turn acquired by Cypress in 2008.
And so I give you ...
http://www.cypress.com/?docID=34302
There is a good chance that this STK12C68-5 chip can be popped into an
MP-1, eliminating the battery. (As you can see, it has an "STK" part
number: this was a Simtek part.)
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