Nintendo 64: eeprom
As everybody knows (?) the standard 512 bytes EEPROM has 2 commands, allowing read and write of the data:
user -> 0x04 <page>
eeprom -> <8 bytes>
which reads 8 bytes from the page <page>.
user -> 0x05 <page> <8 bytes>
eeprom -> <status>
which writes 8 bytes to the page <page>.
Now, with the 512bytes eeprom, the page ranges from 0 to 63; technically the <page> allows for up to 256 pages which would mean 2048 bytes -- the size of the "larger" eeprom... Is this the case?
That is a 2K eeprom behaves like the 512Bytes, with more pages or it has a different command set?
The eeprom also responds to the 0x00 command with the status 0x00 0x80 0x00. The 2k eeprom does the same?
You just need a scope and some patience, if you have a logic analyzer is even easier (I don't have that...). The EEPROM protocol is very simple and not very fast, so it's easy to follow (being a synchronous protocol you also have the triggering clocks...)
The EEPROM is accessed thru the <pif> memory like the controller pads, but I have never understood how you address the eeprom (the joypads are addressed by the offset inside the pif memory)...
Well, the PIF memory is located at 1FC007C0. To find the instructions which write this, you can search for LUI reg,1FC0, which is coded as 3Cxx1FC0 in hex. I will point out that that particular sequence (3Cxx1FC0) appears 6 times in Mario64 and 5 times in Pod Racer, so it should not be hard to locate the relevant sections of code and disassemble it to see how it works.
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yes that means u can write a max of 2048 bytes. but i think most eeproms are 1024 or 512. not sure about that. But these larger chips return a status of 00c0000 instead of 008000.
As for mempack eeprom, contact me on efnet and i'll try to explain it.
-LaC-
