Replacement for MC68701U4 without having the source for the eprom? (only got the compiled 4k bin)

[stefan_nordkvis]

Hello!

Newcomer from Sweden here :smileyhappy:.

I would like to replace a old MC68701U4 for a redesigned pcb but I dont have the original source, only the 4k bin file for the eprom. 

Would it even be possible or am I just wasting my time looking? I saw a similar post about replacement and MC68HC11 family was mentioned and also the newer S12 serie, since theyre both code/instruction compatible.. But he has the source code, I do not. The internal ram reads/writes could be troublesome is the replacement aint got ram in the same area, or if I could use external ram/eprom perhaps with a compatible MCU.

Any input is welcome!

Thanks for reading!

[tonyp]

I couldn't find whether the 68701 is object code compatible with the 68HC11 which would be the primary requirement since you don't have the source.  It can't be compatible with 68HC12 as this is not compatible to the earlier 68HC11 which is closer (historically) to the 68(7)01.

Regardless, from a quick look, the memory map is certainly different, e.g. registers at $0000 -- 68HC11 could have them moved there, vectors at $BFF0, and so on.  This is a significant problem.

The registers are most likely not at the same offsets from zero even if relocated from 68HC11's default of $1000, and they are very likely not functionally compatible, so I would say, your chances are very-very-very-very slim to get this binary working on a different MCU without significant modifications (patches) to the original image.

But, for this you would first need to disassemble and understand the code.  But, if you have to do that, then it'd be a simpler task to just rewrite it (having the disassembled source) for another CPU (I'd go with the 9S08) than to patch the original binary.  4KB of code should not be too hard to disassemble correctly but it would still be non-trivial work.

Another option would be to recreate the same functionality into a newer controller.  Forget how the original did it, just get it done again for another MCU.  For just 4KB of binary the complexity of the original code cannot possibly be that much, and possibly it would be less work overall.

Your final option would be to write an emulator for the 68701U4 that will run on a faster CPU of your choice.

[stefan_nordkvis]

Hello and thanks for the reply!

hmm... I have to give it some more thought. You have some good points and I am tempted to go the:

9S08

or

"Forget how the original did it, just get it done again for another MCU"

route..

Will dive into the 9s08 datasheet tonight and se how I feel :smileyhappy:.

I do have some 68701U4s availible but the rest of the board will be made from active parts so it feels so-so to include a oldie (but goodie! :smileyhappy:).

Althou there is a chance that there will be a FPGA present onboard and the 6801 is availible as a softcore.. one might wonder how much extra work it would be to add u4 functionality to that core.

Have a nice evening, and please let me know if you have any other nice inputs or ideas to share :smileyhappy:

[stefan_nordkvis]

Just found out about this also, DASMx Version 1.40, might be worth checking out in the convertion process.

A quick glance didn't show me any support for the 68701U4 enhanced version but who knows..