DESCRIPTION
The LS138 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 LS138s and one inverter. (See Figure a.) The LS138 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. TRUTH TABLE INPUTS E1 H X X L L L L L L L L E2 X H X L L L L L L L L E3 X X L H H H H H H H H A0 X X X L H L H L H L H A1 X X X L L H H L L H H A2 X X X L L L L H H H H O0 H H H L H H H H H H H O1 H H H H L H H H H H H O2 H H H H H L H H H H H OUTPUTS O3 H H H H H H L H H H H O4 H H H H H H H L H H H O5 H H H H H H H H L H H O6 H H H H H H H H H L H O7 H H H H H H H H H H L H = HIGH Vo...
Motorola
