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.)