11 May
2023
11 May
'23
7:41 p.m.
I thought about this, but the KIM is a pretty simple
system. The only memory
mapped device in that range (really, on the entire unit) are the RIOTs, and
their RAM at $1780 is fine and does not echo.
The KIM only does address decoding for 8K and echoes the rest, so the same
fault is mapped at $2280, $4280, etc. I would think this would still suggest
data is the problem.
I suppose I could randomly replace the RAM and see what changes but again it
seems weird to have a fault so neatly aligned and only in a specific range.
With a simple step through program,
*=$0000
r=$0280
inc w
lda w
sta $f9
sta r
sta r+1
lda r
sta $fb
lda r+1
sta $fa
jsr $1f1f
jsr $1f6a
cmp #$12
bne *-8
jsr $1f1f
jsr $1f6a
cmp #$15
bne *-5
jmp $0000
w .byt 0
it's actually an artifact of the monitor that the upper 6 were clear. Actually,
the stuck bit is entirely bit 2 (i.e., it goes
0 1 2 3 4 5 6 7 8 9 a b c d e f
0 1 2 3 0 1 2 3 8 9 a b 8 9 a b
and the high nybble is OK). Now that sounds more like a bad RAM chip, but why
would it be *just* those addresses? Does that sound like a plausible failure mode?
--
------------------------------------ personal: http://www.cameronkaiser.com/ --
Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser(a)floodgap.com
-- God made the integers; all else is the work of Man. -- Kronecker -----------