27 Oct
2017
27 Oct
'17
1:13 p.m.
On 2017-Oct-27, at 12:13 PM, Ethan Dicks via cctalk wrote:
On Fri, Oct 27, 2017 at 11:40 AM, Dave Wade via
cctalk
74S is faster than 74LS, 74LS was combining low power techniques (which result in loss of
speed) with Schottky technology to get some of the lost speed back, to get a better
speed-power product than 'normal' TTL.
The chronological order of development was 74 --> 74H & L --> 74S --> 74LS
The odd thing is that ic A9 appears to be a
74S151 not a 74LS151. I
wouldn't expect this to work, but I assume it was working at some point in
time!
I don't think that should be a problem. 74S is often a sub for 74LS
when the higher speed of 74LS is not required but the higher drive of
74S is (and the higher power consumption of 74S is irrelevant
in-circuit). There are many times when you can put a 74S where it
calls for a 74LS but often you can't sub 74LS for 74S where it's there
intentionally.
-ethan