3 Jun
2006
3 Jun
'06
4:50 a.m.
On Saturday 03 June 2006 03:31 am, William Maddox wrote:
Roy J. Tellason wrote:
Now that you mention it, that early TTL book didn't have any AND or OR gates
in it, either...
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
I've been wondering for a while now what the
major use was of those
"AND-OR-Invert" gates, since the early TTL stuff I became familiar with
first had a bunch of them in the databook...
Anybody know?
This particular configuration of gates comes up frequently in digital
logic, and combining gates in this way provided more gates with fewer
packages. The 7451, using 2-input AND and OR gates, was often used as
a dual 2-to-1 MUX with unencoded select inputs. The inversion of the
output was not so much a feature as consequence of the fact that an
inverted output was easier to provide, e.g., NAND and NOR are more
commonly used than AND and OR for this reason. NAND and NOR are
also in some sense more universal -- you can compute any boolean
function with sufficient numbers of either NAND or NOR gates alone, but
not with AND and OR, which may require the use of inverters as well.