12 May
2023
12 May
'23
8:46 a.m.
On 5/11/23 21:41, Cameron Kaiser via cctalk wrote:
If the failure affects the EPROM monitor,then any results
you get from the monitor are suspect.
And, the c,d showing as 8,9 also fits the pattern of bad
locations reported earlier!
Jon
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?