The JECS “A12-281001” is found in Nissan Primera P11GT and seems to be identical to the JECS “A12-280 000” found in Nissan Silvia 200sx S14a but with a different firmware. Because of the memory technology used for the ROM (OTP) the firmware can only be written once, the chip is labelled with an ID identifying the firmware but the hardware is perfectly identical.
Used with the same processor but for earlier Nissan Primera/Silvia the M6M72561J IC made by Mitsubishi looks physically identical, the pinout is also compatible but not the ROM size, the M6M72561J is 32K ROM long and the A12-28xxxx is 48K ROM long. I contacted Renesas (Hitachi, Mitsubishi & NEC) to ask if Mitsubishi made an IC with larger ROM memory but they didn’t.
As you can see there isn’t any logo or clue about who made the chip, I found the memory mapping by analyzing the firmware but still didn’t know who made the chip !
This chip is more than a simple ROM memory, there is also a RAM bank and memory mapped digital I/Os counter and PWM capable. It’s an all-in-one memory and I/O expander.
The only one solution is DIE inspection but to access to the DIE first I have the decap the IC. Laser helps me a bit but the nitric acid was more helpful (but takes more time)
Unfortunately the IC is damaged (pin, bounding, etc.) but not the DIE and here is what I found:
Please read “NEC” not “NFC”, so it’s a NEC IC potentially named D29501 ! Thanks to my amscope metallurgical microscope !