Reverse engineering of these boards is a difficult process and I need all the tools I can get my hands on. One tool I have not used yet is the 68HC11 bootstrap mode. In this mode, you can download a small bit of code into the internal RAM and execute it. Care needs to be taken to ensure the code defaults chip selects and things like that so that other parts on the board won't fight each other but in most cases GM defaulted all these with resistors anyway.

The process for loading is quite simple... The binary code you want to put in ram is pre-fixed with a single $FF character and sent to the serial (aldl). I need to do a bit more checking of the configuration of the serial connections to make sure this can all work out. It is important that when you are bootstrapping one side (E or T) that the other side doesn't try to chat... that would mess up the download for sure.

Please don't attempt this unless you are sure of what your doing. The HC11 reference manual goes into complete detail on the use of this mode. Myself I am trying to decide if to use this or use the built in download and execute through the EL327 clone.

I have two photos to show where the mode lines are. If pulled to low when reset is released, the part will enter bootstrap mode. I have used this technique with success for my Optispark simulator.

It looks to me like this could be used to resurrect a bricked module without de-soldering the FLASH part.

Second picture is full of glare, but you can make out the locations. I will re-take that photo for future work

-Tom

RB_SS.jpg
GB_SS.jpg