74ACT138SC datasheet(3/11 Pages) ONSEMI

3 / 11 page

www.fairchildsemi.com

Truth Table

= HIGH Voltage Level

= LOW Voltage Level

= Immaterial

Functional Description

The AC/ACT138 high-speed 1-of-8 decoder/demultiplexer

accepts three binary weighted inputs (A0, A1, A2) and,

when enabled, provides eight mutually exclusive active-

LOW outputs (O0–O7). The AC/ACT138 features three

Enable inputs, two active-LOW (E1, E2) and one active-

HIGH (E3). All outputs will be HIGH unless E1 and E2 are

LOW and E3 is HIGH. This multiple enable function allows

easy parallel expansion of the device to a 1-of-32 (5 lines

to 32 lines) decoder with just four AC/ACT138 devices and

one inverter (see Figure 1). The AC/ACT138 can be used

as an 8-output demultiplexer by using one of the active

LOW Enable inputs as the data input and the other Enable

inputs as strobes. The Enable inputs which are not used

must be permanently tied to their appropriate active-HIGH

or active-LOW state.

Logic Diagram

Please note that this diagram is provided only for the understanding of logic

operations and should not be used to estimate propagation delays.

FIGURE 1. Expansion to 1-of-32 Decoding

Inputs

Outputs

HHH

LLL

HHH

74ACT138SC Datasheet(PDF) 3 Page - ON Semiconductor