Build your own Apollo Guidance Computer

Chuck Guzis cclist at sydex.com
Tue Dec 19 20:57:19 CST 2006


On 19 Dec 2006 at 15:41, Guy Sotomayor wrote:

> LS usually has the speed of TTL with the power dissipation of L.
> 
> Other variations:
> 
> 74Hxx
> 74Lxx
> 74Sxx
> 74ASxx
> 74ALSxx
> 74Cxx

74F is another common one.  Normally, one can assume that the 
pinout's the same between all families, regardless of the letters 
after the "74".  The notable exception is 74L--some members of the 
family have pinouts that differ from the corresponding 74/74S/74LS 
ones.   e.g., 74L85 vs. 7485.

Similarly, 74 and 74-followed-by-alphabet-soup ICs can differ in 
implementation.  Some notable examples are 7473--positive pulse-
triggered JK FF; 74LS73 negative-edge-triggered JK FF.

And again, one could get away with wire-OR-in 74L-series logic, which 
would be a disaster in any other 74-series logic family.

Just a gentle reminder to check the databook before cross-
substituting...

Cheers,
Chuck




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