Hi again !
[re: reading Backup RAM directly]
David Michel said...
Enable RAM:
@> lda #$80
@> sta $1807
Disable RAM:
@> lda $1803
@>
@> And apparently a 'csl' is also needed when accessing the Backup RAM,
@> it must be a slow RAM or something like that.
OK, I just tested this out, and I found that the Develo system provides
some interesting utilities.
Here are my results:
I used getbnk and setbnk to set MMR #4 to $F7 (the backup memory segment is
generally loaded into the $8000-$8800 region for manipulation).
I did a dmpram from the $8000 region, and saw the same results as
previously; $80 from the $8000 area, $81 from $8100, etc.
I then used edtram to set $1807 to $80. Then I did a peek at $8000 from
the edtram utility, and saw what appeared to be good memory. Note: I
didn't test the RAM for being able to write to it.
I then did a dmpram from $8000, and it was still unlocked.
After doing several tests, I found that David was correct about the RAM
being re-locked after performing a read. But I found that a read to $1807
was all that was necessary to re-lock the RAM.
>>I seem to recall that enabling is succesive writes to $1407 - 3 specific
>>bytes, I think ?
>
> Hmm strange, that sounds familiar, I already heard of this 3 bytes
> sequence, but I can't remember where...
The 3-byte sequence is what I had seen when writing my emulator, and
trapping accesses to $18xx memory areas. Sokoban World and Bomberman both
do this 3-byte access, if my memory serves me well, and I know that one
byte had the $80 bit set, but I think one of the other bytes was $43...