Well, as I've been in contact with Cyrille, and found him to be genuinely intersted in issues relating not only to the 805x but microprocessors/microcontrollers in general, and that may yield a bit of insight.

I don't think it matters WHERE the value of 0x00 is stored, so much as what happens in an 8-bit system when it's decremented. It's already been stated, and quite correctly, that this is going to be 0xFF, which you can interpret as 255 decimal or as -1 in two's complement.

It is true, that one should, generally be more specific about such a question. However, Cyrille is in an environment where his instructors are making do with limited understanding of the subject matter and, therefore, are apparently unable or ill-equipped to explain such matters.

I think, under the circumstances, we should allow him some leeway in expressing his query. His question, however, has been answered, I believe.

Andy has it right, though, in that I believe Cyrille was asking what happens when you decrement from zero, irrespective of the location in the memory space.

RE