[cctalk] Re: KIM-1 stuck bits from $280 to $29f

11 May 2023

...
   Odd fault on
my Rev D KIM-1 popped up while writing code this afternoon
 (initially I thought I had a bug in my paper tape transmitter) - between $0280
 and $029f, the upper 5 bits are stuck at zero. The rest of the address range
 seems fine. In particular, $0080-$009f, $0180-$019f and $0380-$039f work
 correctly.

 This doesn't smell like a bad RAM chip to me or I would think there would be a
 bad bit throughout the entire 1K, so I suspect this is a data bus problem but
 I'm not sure where to start looking. Any guesses from the group?
  Maybe an I/O device is sending on the bus when it should not be.  Are there any
 devices that have a register range of XX80 to XX9F? 
(By the way, I had a typo in my message: it's the upper *six* bits, not five.)

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.

-- 
------------------------------------ personal: http://www.cameronkaiser.com/ --
  Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser(a)floodgap.com
-- "I'd love to go out with you, but my personalities each need therapy."
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[cctalk] Re: KIM-1 stuck bits from $280 to $29f