From what understand, there is a ROM chip used on the P4 ecms. I'm not talking about the prom but a ROM chip, on or working with the mcu. According to the M68hc11 reference manual, the ROM is used to store the program instructions. Then it goes on to say that the ROM can be disabled and all the instructions can be stored in the EPROM, is that right? If so then does our ECMs disable the ROM (for running the program) and rely on only the EPROM?

I was thinking that $6E, $8D (etc) are all ROM masks?

 

I guess that was another dumb question and that is why nobody answered it,heh?

 

I would imagine the reason there was no reply is because nobody knows for sure. I think the vast majority of people believe (and are correct that) the P4 microprocessors were made to GM/Delco's specifications. I would imagine the only person(s) who could really answer this would be someone who worked for either company when the ECMs were being designed.

My *guess* would be that the goal to cut costs would drive them to make a chip without onboard ROM since the programs and cals were always going to be on an EPROM.....

 

To my knowlege, the ROM is your PROM, and the EEPROM is internal to the generic MPUs. The ones supplied with the ecms arn't generic and may very well not have it.

 

THe inference is that you know GM used customized M68HC11 processors. If so then how do you know for sure?









...maybe it would help if somebody explained the term "MASK" to me. I'm talking specifically when used with $6E/$61/$8D(etc).

 

It's hard for me to believe that even RBob doesn't know.

 

The custom part comes from the fact that the addresses of whats in the cpu seems to deviate quite a bit from whats listed in the reference manual with some of the ecms.

Those bytes you mentioned are the ID bytes for the code running on the ecm. Doesnt really mean as much on the later ones but on the C3 ecms the ID byte was used to make sure the correct prom was used since part of the code was internal to the ecm on roms and the calibration and the rest of the code was on the prom. The ecm would activly check the ID byte ($61, $4D, $42, etc.) to make sure it had the right prom installed.

 

What reference manuals are you referring to?

It's seems to me that "if" you are correct then the P4 MCU's are specific for each ECM. From what I understand, there is only one way to customize the M68HC11. That is to silicon wafer a photographic (rom) image on to the MCU. Maybe I should try to install a mcu from a 165 into a 730 ecm to verify.

 

The one you where referring to, the manual from moto.

 

Hmm, I'll check into that..