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Registered Member #546
Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239
Does anyone know what the HC designates in an IC? I have a drawer full of RS7474N DIP-14 D type + edge triggered f/f's I'd like to sub in a circuit that calls for the 'HC' variety. (MC74HC74).
My limited understanding is that most ICs with the same numbers vary little in function from manufacturer to manufacturer, but it certainly can make a world of difference when characters are added - no matter how minor, right?
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
If my memory does not fail it stands for High-speed CMOS. That means that the input and output voltages are different (among other things).
A 74HC74 should be able to drive a TTL chip but a TTL chip can't drive a HS chip since the TTL chip does not have high enough output voltage. You might get by with a pull up resistor in some cases. A 74HCT74 will on the other hand be voltage compatible with a TTL chip.
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IC substitution: RS7474N for MC74HC74?
