18 Dec
2010
18 Dec
'10
5:29 p.m.
but the speed, temperature range, etc. requirements
for a desktop calculator are not that high.
I think you (or maybe someone else) may have hit it earlier with the suggestion of
fan-out/fan-in requirements and maybe some specializations such as open-collector wired-or
with built-in pullups at the receiving end.
Later 7400 series chips for specialized functions (e.g. verge of SSI and MSI) had
not-really-TTL-compliant inputs and outputs for specialized daisy-chain or low-fanin-load
purposes. Look at the BI/RBO pin of a 7447 etc. (It's an input AND an output! Wow!)
It's easy to see how this could be applied to some of the "stock" standard
logic functions to greatly cut pin counts for a desktop calculator, and I suspect
that's what the unique numbers are for.
Tim.