4009 Hex Inverting Buffer

A CD4009 CMOS integrated circuit providing a hex inverting buffer. Six inverting buffers that also shift levels down from higher voltage logic, historically used to interface CMOS to TTL. Being 4000-series CMOS it runs on anything from 3 to 18 volts, which makes it far more flexible than 5V-only TTL logic and lets it work directly in battery and higher voltage circuits. It also draws almost no current when idle. The trade-off is speed: CMOS of this family is slower than 74HC logic, so it suits control, timing and teaching applications rather than fast data paths. Unused inputs must be tied to a supply rail, never left floating.