The 74HC138 is a high-speed Si-gate CMOS device and is pin compatible with Low-power Schottky TTL (LSTTL). The 74HC138 decoder accepts three binary weighted address inputs (A0, A1 and A3) and when enabled, provides 8 mutually exclusive active LOW outputs (Y0 to  Y7). The 74HC138 features three enable inputs: two active LOW (E1 and E2) and  one active HIGH (E3). Every output is HIGH unless E1 and E2 are LOW and E3 is HIGH. This multiple enable function allows easy parallel expansion of the 74HC138  to a 1-of-32 (5 lines to 32 lines) decoder with just four 74HC138 ICs and one

inverter. The 74HC138 can be used as an eight output demultiplexer by using one of  the active LOW enable inputs as the data input and the remaining enable inputs as  strobes. Permanently tie unused enable inputs to their appropriate active HIGH- or  LOW-state. The 74HC138 is identical to the 74HC238 but has inverting outputs.