lab4 .pdf - CPSC 121 Models of Computation Lab#4...

CPSC 121: Models of Computation
Lab #4: Time-Division Multiplexing
Objectives
In this lab, you will be introduced to the method of time-division multiplexing which uses a type of circuit called a
demultiplexer. You will also learn about the Arithmetic Logic Unit and see how multiplexers are used within it.
1 Pre-lab
Imagine you are calling a friend in Asia. While you are talking, there is one signal connecting you and your friend.
However, it would be too expensive to directly wire every telephone in North America to every telephone in Asia. Laying
one wired connection across the Pacific Ocean is expensive enough.
Have a look at the animation at multiplexer system.gif . Here we see a
solution for wiring telephones in North America to telephones in Asia: have one wire between the continents, and connect
telephones from the two continents to either end of this one wire, as needed for conversations. (This technique is known
as time-division multiplexing. )
TODO (pre-lab): In the animation, five conversations are being connected. Draw what it would look
like if six conversations were being connected.
The connection scheme in the animation uses a circuit called a demultiplexer to undo the effect of the multiplexer. The
multiplexer selects the caller’s signal and passes it to the demultiplexer, which then selects the appropriate receiver to
send the signal to, thus connecting the two friends.
A 1-to-2 demultiplexer has two inputs: s , analogous to s (select) in our multiplexer, and y , an input wire.
It produces two outputs: x0 and x1 , the demultiplexed signals. It works like this:
• When s = 0, x0 outputs the value of y , and x1 outputs LOW.