74HC138D,653

The 74HC138; 74HCT138 decodes three binary weighted address inputs (A0, A1 and A2) to
eight mutually exclusive outputs (Y0 to Y7). The device features three enable inputs (E1, E2 and
E3). Every output will be HIGH unless E1 and E2 are LOW and E3 is HIGH. This multiple enable
function allows easy parallel expansion to a 1-of-32 (5 to 32 lines) decoder with just four ‘138 ICs
and one inverter. The ‘138 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. Inputs include
clamp diodes. This enables the use of current limiting resistors to interface inputs to voltages in
excess of VCC.