> 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 * ckai...@floodgap.com -- God made the integers; all else is the work of Man. -- Kronecker -----------