CSE370 Laboratory Assignment 4
Using Multiplexors to Implement Boolean Functions
Distributed: April 15
Due: By the end of lab session (4/18,19)
Objectives
In this lab assignment, you
will use multiplexors to implement an adder.
You can get a head start on the
Lab by designing and simulating the circuit for Step 2 (and Step 6 if you are
interested in extra credit).
Tasks
- The multiplexor (also known
as a selector) is a very powerful component that is typically used to
select one of several inputs to connect to the output. In this exercise, we will use this
capability to implement functions directly from a truth table instead of
with gates. The ‘153
multiplexor chip contains two 4-1 multiplexors that share the same select
inputs. Be sure to use the chip maps as a
guide to the pinout, and notice that each multiplexor has an enable
signal. Instead of using simulation, wire up one of the multiplexors of
the ‘153 on your prototyping board to switches and lights. Connect each of the four inputs, the two
select inputs and the enable to switches, and the multiplexor output to a
light. Using the switches, show
that the multiplexor works as advertised.
- Now use ActiveHDL to design a
full adder using a single ‘153 chip, using one 4-1 mux to implement
each of the carry and sum functions. You will need to add an inverter as
well. Now create a top-level test circuit schematic as you did in Lab 3,
using the test
fixture given in the tutorial to test your design. Don’t forget
to connect the enables!
- Now implement this full adder
circuit using your prototyping board.
Connect the inputs to switches and the outputs to lights. Be sure
to plan ahead – you will need another ‘153 chip for part
4. HINT: If
your circuit is not working as expected use the logic probe to trace
through the circuit to help you identify any wiring errors.
- Now design a two-bit
ripple-carry adder using two of the full adders you designed in part 2.
You will simply make two copies of the same circuit and connect them
together. Note that this adder will generate a 3-bit output.
- Show the simulation results
and the working circuit to a TA and have them check you off as having
completed this laboratory assignment. They will ask you to show them your
work and explain your design files and circuit. Hand in your schematics for parts 2 and
4. Do not hand in waveforms this time.
- [Extra Credit – only if
you have lots of spare time!] Turn
your circuit from #5 into a 2-bit ALU that can both add and subtract. That is, add a control input: if it is
0, then the circuit adds and if it is 1, the circuit subtracts. If you are very clever, you can
implement this using just 3 chips!
NOTE: The gates in your Active-HDL
solution must exactly match the gates used in your
prototyping board solution.