System EEPROM - Block L


        These two CAT25C256 256k-Bit (32kx8) SPI Serial CMOS EEPROM take care of the system's non-volatile memory needs.  The MPC555 Microcontroller has more than enough RAM on board, especially for a program like ours which is totally written in assembler (no huge library tag along or clunky spaghetti C code here).  There is an EEPROM on board the MPC555 but it has an unreasonably low number of write cycles limitation.  Something in the order of 50 writes!  These guys are over 100,000 write erase cycles.  All three will be used though.  The internal MPC555 EEPROM will be used as the boot loader.  Just enough smarts to configure the SPI interfaced to U1000 where it then reads in the real operating code.  The rationale here is that after initial debug the boot loader EEPROM will not have to be changed, or very rarely at least, and all the development and operational code will be stored in U1000.  The second EEPROM, U1001, will primarily be used for a non-volatile scratch pad area.  Things like learn mode results and/or the air fuel maps for the particular motor.