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Not so easay to seperate the pins. They are linked under the MCU.
It is a shame they did not link them on the outside of the MCU, or use 'expensive' pullup resistors on the unused pins

There must be two different style boards, the 4 808s I have are all external to the MCU

Cool,
The one I removed the MCU from was an early version with date codes of 85 - 86 on the chipset.
Have you had a look at the VR/VS units?
I will have to go through my stockpile........

You are right again VL400. Most of my other 808's give external access to the unused I/O pins.
I have a 25LC1024 SPI EEPROM on it's way. 128K bytes. 10 bytes at 10 samples per second = ~20 minutes worth of logging.
10 bytes should cover the basics. Would be nice to trim it down a bit to extend the logging time if possible.

Split the topic as it went off track from the nintendo logging and thought it deserved its own topic! Am looking forward to seeing what can be made of using an internal EEPROM, would be very handy


The VR/VS manual ECMs I have seen also have external tracks to cut, but I would be too scared to cut them! I stick to the el cheapo 808s!

Had a look at the info I have but am still not sure what bit 6 does (no reference in code and just the loop on the PCB). Bit 5 is the fault line from the high current driver ICs, its used as feeback incase of a fault with them I think. It looks like GM did not equip the software to use it on the 808s, the later VR auto PCMs do use a function like this. In the past I have used bit 7 as a kind of free time indicator when testing the major and minor loops (scope it to see what the remaining time for the interrupt period is), so I know that one is free to use and works.

As the only reference to these bits is the DDR register, we should be able to use one/both of the 2 pins configured as inputs safely.
It is interresting that these 3 I/O bits are connected to the FMD, Quad drivers and a pin marked as "poweroff" on the PSU IC. I wonder if this was used for a standby mode, possibly initiated by external debug code?
I will isolate the 3 pins on an old 808, and see if I can crash it......

make sure your wearing your seatbelt

Just had a thought.
If we invert a PLCC socket over the MCU, we get easy access to all of the pins required for a Serial EEPROM conversion.
The socket is a nice fit. 6 wires to the chip, cut the I/O trace on the main board. Job done. 128K logger for under 20 bucks!
Would also be a nice solderless way of adding RS232.
May need a bit of double sided tape on the MCU to stop it vibrating off.

theres no doubt about it ucmatt, your an ideas man

hehe this forum has definatly stirred up some good thoughts and processes in its short life and its only destined to get better. good work on nutting that out matt thinking outside the square is allways good for something.