Multiplexor


Chooses one input from many and copies it to the output.


Common configurations are:


4 inputs - 2 address lines

8 inputs - 3 address lines


The Output Enable line is the same as before


The truth table becomes unwieldy with so many variables, and is mostly empty, so we cut out all the uninteresting cases:


C1 C0 Q

0 0 0 I0

0 0 1 I1

0 1 0 I2

0 1 1 I3


Q = OE ( I0 + C0I1 + C1I2 + C1C0I3)




Demultiplexor


1 input is copied to one of several outputs


Common configurations are:


1 input - 2 address lines - 4 outputs

1 input - 3 address lines - 8 outputs



Consider the decoder. It is equivalent, if we replace the input with OE



159.233 Lecture 3 -