From Osiris
At the core of the ECU is a processor that uses 3 types of memory:
- Flash-ROM (internal to the processor). This is Read Only Memory, where the ECU stores its operating software as well as the tables that are used to calibrate/tune the ECU’s operation. This area can only be written to via an ECU reflash (Osiris). The flash memory has a limited number of rewrites that can be preformed before the memory starts to degrade. Once the flash memory has begun to degrade the ECU will have to be replaced. A minimum of 200 flashes can be preformed according to the CPU data sheet, but twice that is likely possible (we flashed the ECU on our development 350Z more than 400 times without any memory degradation).
- RAM (internal to the processor). This is Random Access Memory (read and write) that the ECU software uses to store variables that change in real time such as sensor readings, environmental conditions and changes over time, as well as calculated values that are used for the software control models that manage engine operation.
- Non-volatile EEPROM (external from the processor). This non volatile memory is used to store things like idle adjustments, ignition adjustments, learned idle air volume, VIN, and other static values that vary from vehicle to vehicle. You should not have to deal with the EEPROM, but it’s good to know it’s there.
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