Hi all,

There used to be a batteryless mod for the MP-1, but it's
proving hard to find.

What this does is eliminate the need for the coin battery
which preserves the presets when the power is off, by supplying
voltage and a tiny trickle of current to the so-called Non-Volatile
SRAM chip.

This is not to be confused with the "battery mod" which consists of 
soldering
in a battery holder to make the replacement easier, since the battery 
is
soldered to the circuit board!

I'm trying to come up with my own batteryless mod recipe.

My research so far indicates that the RAM chip in the MP-1 conforms to
a widely used JEDEC interface called "Bytewide".  Many 8K X 8Bit chips
have a compatible pinout.

I have found some chips which are "fake" replacements: there are chips
that are the same technology, but which actually have a lithium 
battery
inside the package. They are typically rated with a retention of 10
years. These are awful! Once the battery runs out, you have
to throw out the chip, so the only way to preserve the presets is to 
do
a SysEx dump and restore. Watch out for anything with a suspiciously
low retention time of like 10 years.

However, there exist EEPROM chips which have a compatible pinout and
protocol.  The device they are plugged into doesn't know that it's
talking to an EEPROM rather than an SRAM.

So the task is basically to find one of these chips that work in the 
MP-1.

Intersil (formerly Xicor) has a unit called the X28HC64 that looks
good. It has a 100,000 write cycle endurance, and 100 year retention.
Someone is selling these on eBay, I've noticed.

Other chips can be found by searching for "28C64 eeprom". Atmel
(the company that makes the CPU's used in Arduinos) has one,
but the retention time is lower, something like forty years.
Still, it's not unreasonable.

I'm not sure what, if anything, this will involve, beyond just
removing the old SRAM chip and battery, and popping in the EEPROM.
Hmm ....

Would anyone happen to remember the details of any MP-1
batteryless mod, and what chip was recommended?