11 Apr
2007
11 Apr
'07
9:04 a.m.
I have seen memory TI chips in databooks where you had
to specify
"upper" or "lower" by part number specifically because they were
bonded out differently *to be piggybacked*. The memory dice were
identical - what was different was the pinout, by one pin. It wasn't
an unknown technique back in the day, but it wasn't the favored one.
We had a Qbus COMBOARD that was experimentally altered from 512KB to
1MB by piggybacking a bunch of 50256s on top of the ones that were
already there. Since we didn't have "upper" and "lower" parts,
the
engineers lifted one pin and ran the select line "in the air".
If we could have purchased piggybackable chips, I'm sure we would
have, but they _did_ exist.
Ethan, this is news to me. I work as an electronics' designer for years,
never seen ANY kind of memory made to be piggybacked. But of course, living
is learning. Thanks for the info, I'd be glad if you could supply some p/n /
datasheets for me to take a look. This is an interesting curiosity
Greetings from Brazil
Alexandre