IC Numbering

[russ lavergne]

A follow up question to my last post. Which lettering system is universal
to older IC's. Example. If I buy a 75HCXXX can I swap that into a 74LCXXX
or 74??XXX. Are the HC the latest and completely backward compatible? If
not is there one that is somewhat universal so that if I have a 74LSXXX go
out, I can buy a HC or ?? that will work in it' place? I hope my question
makes sense.

Thanks
Russ

 

[Eric Smith]

russ lavergne wrote:

A follow up question to my last post. Which lettering system is universal
to older IC's. Example. If I buy a 75HCXXX can I swap that into a 74LCXXX
or 74??XXX. Are the HC the latest and completely backward compatible? If
not is there one that is somewhat universal so that if I have a 74LSXXX go
out, I can buy a HC or ?? that will work in it' place? I hope my question
makes sense.

There isn't any other 74 subfamily that is a universal replacement for
the others. That's why the still make so many different ones.

The 74HC parts usually cannot substitute for 74LS parts due to the high
Vih input threshold. 74HCT is more likely to work as a substitute for
74LS, but there is no guarantee as the timing is not the same.

Generally if you have a failed 74LS part, the replacement should be 74LS.