HC vs. HCT

ON Semiconductor’s High–Speed CMOS product family, intended to give the designer an alternative to LSTTL. HSCMOS, with the faster speed advantage over metal–gate CMOS (MC14000 series) and the lower power consumption advantage over LSTTL, is an optimum choice for midrange designs. With the availability of high–speed CMOS microprocessors and memories, the ability to design a 100% CMOS system is possible.
HCT devices offer a short–term solution to the TTL/NMOS–to–CMOS interface problem. To achieve this interface capability, some CMOS advantages had to be compromised. These compromises include power consumption, operating voltage range, and noise immunity.

In most cases HCT devices are drop–in replacements of TTL devices with significant advantages over the TTL devices. However, in some cases, an equivalent HCT device may not replace a TTL device without some form of circuit modification.
Designers can use HCT devices to perform logic level conversions only. In newer designs, the designer wants all the advantages of a true CMOS system and designs using only HC devices.