11 May
2023
11 May
'23
7:52 a.m.
On 5/11/23 00:53, Cameron Kaiser via cctalk wrote:
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?
That probably needs the XX to be something like FF for
proper operation, but if the gate that decodes that part of
the address has failed, this might be what you would see.
Jon