4.5 TTL Logic Family

The TTL logic family consists of several subfamilies or series. Shown in Table 1 is a list of TTL series together with the prefix designation used to identify the subfamily and example ICs. The differences between the various TTL series are in their electrical characteristics such as power dissipation, delay times, and switching speed. However, the pin layout and logic operation performed by the internal circuitry is the same regardless of the subfamily name.

TTL Series	Prefix	Example IC
Standard TTL	74	7404 (hex inverter)
High-speed TTL	74H	74H04 (hex inverter)
Low-Power TTL	74L	74L04 (hex inverter)
Schottky TTL	74S	74S04 (hex inverter)
Low-power Schottky TTL	74LS	74LS04 (hex inverter)
Advanced Schottky TTL	74AS	74AS04 (hex inverter)
Advanced Low-power Schottky TTL	74ALS	74ALS04 (hex inverter)

Table 1. Summary of TTL Subfamilies