🚀 go-pugleaf

Here's what I know off the top of my head about some of the TTL
(and other logic) families around these days.

Jargon: TTL = Transistor Transistor Logic

7400	The original series. Evolved from DTL (diode transistor logic)
        giving higher speed.

74H	This is TTL with gold doping and decreased internal resistances
        in the output stage. This creates a faster, higher powered device.

74S	This family uses the Schottky transistor. These devices do not
        have saturated output stages, and thus can switch much faster
        than normal TTL.

74LS	Here the device uses the Schottky transistors, but the internal
        resistances are increased to reduce power consumption. The parameters
        are juggled to generally give slightly better speed at reduced
        power levels as compared to 7400.

74F	This is the best of the wonder chips. Fairchild applied their
        expertise to bipolar, giving near-ECL speed at near-LS power
        levels to TTL. Motorola junked the ALS/AS stuff to follow
        Signetics and Fairchild/(National) with this family.

74ALS   TI's attempt at bettering LS. Obsolete with 74HC/HCT.

74AS    TI's attempt to combat the 74F series. It loses.

74C     National brought this family out to give designers the familiar
        TTL pinouts in a CMOS logic family. RCA had a CMOS line, but the
        brain-damage of figuring out the 4000 pinouts was a lose...

74HC    This family is CMOS upgraded with modern processing techniques
        to attain higher speeds than regular 74C.

74HCT   This is 74HC fully spec'ed to replace 74LS. Actually, at higher
        frequencies, HCT dissipates >>more<< power than LS, so beware...

--Steve