On Fri, 1 Nov 2013 00:35:07 -0400, you wrote:
>So I can generally replace a 7404 with a 74LS04 without any problems?
*Normally*, yes, but there *are* cases where you can run into problems. The
switching speed of 74LS-series parts isn't *quite* identical to standard
7400-series; the propagation delays of a 7404 vs. a 74LS04, for example:
-------- 7404 -------- ------- 74LS04 -------
tPLH 12ns (typ) 22ns (max) 9ns (typ) 15ns (max)
tPHL 8ns (typ) 15ns (max) 10ns (typ) 15ns (max)
(Source: a very dog-eared and well-used copy of "The TTL Data Book, vol.2",
Texas Instruments, 1985)
The difference is, admittedly, pretty small, but it can add up when you've
got signals flowing through a bunch of different gates, or when you've got
a more complex chip (such as the 74191). So, depending on the circuit in
question, there's a small (but non-zero) chance that you *could* end up
with a "race" condition by swapping a 74LS part into a circuit full of
7400-series chips.
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solarfox@triluminary.net (Gary Akins jr.)
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Received on Fri Nov 1 08:44:34 2013
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