CMOS USAGE RULE

Many parts in the CMOS HC, AC, and FC families are also offered in "T" versions (HCT, ACT, and FCT) which have input thresholds that are compatible with both TTL and 3.3 V CMOS signals.  The non-T parts have conventional CMOS input thresholds.

The 74H family is the same basic design as the 7400 family with resistor values reduced. This reduced the typical propagation delay from 9 ns to 6 ns but increased the power consumption. The 74H family provided a number of unique devices for CPU designs in the 1970s. Many designers of military and aerospace equipment used this family over a long period and as they need exact replacements, this family is still produced by Lansdale Semiconductor.[23]

The 74S family, using Schottky circuitry, uses more power than the 74, but is faster. The 74LS family of ICs is a lower-power version of the 74S family, with slightly higher speed but lower power dissipation than the original 74 family; it became the most popular variant once it was widely available.

The 74F family was introduced by Fairchild Semiconductor and adopted by other manufacturers; it is faster than the 74, 74LS and 74S families.

Through the late 1980s and 1990s newer versions of this family were introduced to support the lower operating voltages used in newer CPU devices.

Characteristics of selected 7400 series families[24]
Parameter 74C 74HC 74AC 74HCT 74ACT Units
(VDD = 5 V)
VIH (min) 3.5 2.0 V
VOH (min) 4.5 4.9 V
VIL (max) 1.5 1.0 1.5 0.8 V
VOL (max) 0.5 0.1 V
IIH (max) 1 μA
IIL (max) 1 μA
IOH (max) 0.4 4.0 24 4.0 24 mA
IOL (max) 0.4 4.0 24 4.0 24 mA
TP (max) 50 8 4.7 8 4.7 ns


List of 4000-series integrated circuits"

List of 7400-series integrated circuits"

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