74xx

74xx refers to a large family of integrated circuit logic devices known as the 7400 series. Originating in the 1960s from Texas Instruments, these devices typically contain several gates or other logic functions in a single package, most commonly a 14-pin DIP. Device numbers such as 7400, 7404, 7408, and 7432 denote specific functions (NAND, inverter, AND, OR) within the same family.

Subfamilies differentiate the technology and electrical behavior. The original devices are TTL-based, while CMOS variants such as 74HC, 74HCT, and 74AC/74ACT use CMOS processes. 74LS and related parts are low-power Schottky TTL. 74HCT models provide TTL-compatible inputs, facilitating interfacing with older TTL logic.

Electrical characteristics vary by family. Classic 74xx TTL parts typically run from 4.75 to 5.25 V with moderate power and fixed input thresholds. 74HC/74HCT parts usually operate from 2 to 6 V, with higher input impedance and faster switching. Outputs are suitable for moderate fan-out, and each device specifies drive capability and propagation delay in its datasheet.

Packaging and use. The 14-pin DIP is common, but many parts are available in small-outline or other packages. The 74xx family is widely used in education, prototyping, and legacy equipment for implementing basic logic, counters, and small state machines. In contemporary designs, CMOS variants such as 74HC and 74HCT are typically preferred for higher speed and lower power, while classic TTL 74xx remains prevalent in existing systems.