19 Dec
2010
19 Dec
'10
6:55 p.m.
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.
That was quite an anomaly in the 7447, but off-hand it is the only IC I
can think of that being done in.