Hey Guys,

Will I be able to safely drive 74LS with 74HC series ICs and/or vise versa? I have read that the logic levels are not quite the same for both series ICs because the HC series is CMOS. How different are the TTL and power consumption levels?

 

Google is your friend. www.fairchildsemi.com/an/AN/AN-319.pdf

 

The short answer is you can drive LS with HC, but the inverse is not true. 74HCT and 74LS are compatible in both directions. In addition, 74HC and 74HCT are compatible both ways.
You have to be aware of fanout limitations in all cases.

You should still read AN-319.