This guide details the procedure for dumping the internal ROM contents of a PLCC68-packaged Oki 66207 microcontroller, often found in certain JDM OBD1 ECUs. The process is similar to the DIP64 reader method, but with specific mapping adjustments for the PLCC68 configuration.

Hardware Modification#

1. ECU Preparation: Ensure the ECU is chipped with a 74HC373 latch, EPROM socket, and a 1k Ohm resistor (R54).
2. Wiring:
   • Connect a wire from MCU pin 17 (A15) to EPROM pin 1. (Do not insert pin 1 of the EPROM into the socket).
   • Connect MCU pin 21 (P2.2) to MCU pin 29 (_EA).
   • Cut the PCB trace on pin 29 and replace it with a 1k Ohm resistor.
3. Setup: Install a 27C512 EPROM programmed with the ROMREADER software into the socket.
4. PC Interface: Connect the ECU to a PC using an RS232-to-TTL converter.

ROM Dumping Procedure#

1. Terminal Config: Configure serial software to 4800 baud, 8 data bits, No parity, 1 stop bit (4800, N, 8, 1).
2. Execution: Power on the ECU. If the address display does not start at 0000, click RESET.
3. Extraction: After approximately 1 second, the address counter will begin running. Wait for the counter to reach 8001.
4. Save: Click SAVE to export the dumped ROM data.

After the dump is successful, remember to solder the cut PCB track to re-enable normal external ROM functionality.