> From owner-qrp-l@Lehigh.EDU Thu Mar 27 08:38:59 1997
> Date: Thu, 27 Mar 1997 10:38:53 -0600
>
> Can some give me a quick answer on the difference between 74HCxxx and 74HCTxxx
> IC's? I'd like to know if I can sub an HCT for an HC?
>
> Thanks and 73 de KA0GKC Claton Cadmus
> E-mail cla@spacestar.net
> TCP/IP ka0gkc@ka0gkc.ampr.org
> Ask me about the Minnesota QRP Society!
> http://www.spacestar.net/users/aplitech/mnqrp/
>
It has to do with the input and output thresholds of the logic family.
An HC part running at 5 volts Vcc has an output that swings
between 0.5 volts and 4.44 volts (CMOS levels). An HCT parts output swings
between 0.4 volts and 2.4 volts (similar to TTL).
The input thresholds are also different, the HC part thresholds
are at 1.5 volts for a low and 3.5 volts for a high. On the HCT parts
the low input threshold is 0.8 volts and the high threshold is 2.0 volts.
What does this mean as a bottom line?
1. You can drive an HCT part with an HC part.
2. You can't drive an HC part with an HCT part.
Hope this helps.
72, Ray WB6TPU
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