18 Mar
2020
18 Mar
'20
6:05 a.m.
It includes a table which says which chip each bit in
the memory is
stored in
Oh, there's an entry (well, actually two) missing from the table, which is the
parity bits (2; byte parity); I'll work them out and add them. (I know, by
elimination, which two columns of chips are the parity bits; I just don't know
which is for the high byte, and which for the low.)
The flippping documentation doesn't say whether it's even or odd parity,
though! I'm assuming odd (which seems to be the usual: probably so that
totally failed memory - all 0's - generates an error), but now that I think
about it, it should be pretty easy to work out. I'll just store a '0' word,
and looking at either parity bit should give me whether it's using even/odd;
storing '-1' should confirm.
Then I can do byte writes to work out which chips the high/low parity bits
are in.
I'm assuming the DEC memory diagnostics (for people using them, not their own)
will call out parity failures, and high/low, so people will know which chips
to replace.
Noel