LAB 4: ALU and CPU

EEL 3701

Department of Electrical & Computer Engineering Revision 
Page 1/5 LAB 4: ALU and CPU
OBJECTIVES
The objective of this lab is to design a simple arithmetic logic
unit (ALU) and then to expand and augment the simple ALU.
The augmentation of the ALU with registers (creating an
RALU) and the addition of several multiplexers will result in
the creation of a simple central processing unit (CPU). The
CPU will be a building block used in a future lab.
MATERIALS
• Your entire lab kit (including your DAD/NAD)
• Useful Quartus Components:
• In “others | maxplus2” library
o 74153: Two 4-input MUX’s (recommended)
o 74151: 8-input MUX (recommended)
o 74283: 4-bit Adder (recommended)
o 7474: Dual D-FF (not recommended)
o 74175: Quad D-FF (not recommended)
• In “primitives | storage” library
o dff (recommended)
• In “primitives | other” library
o vcc, gnd
ARITHMETIC LOGIC UNIT (ALU)
In this part of the lab, you will design a 4-bit ALU (Lab4_ALU).
The ALU has two 4-bit inputs, two function-select inputs, and a
carry input. The ALU has a 4-bit function output and a carry
output as described Table 1, shown in Figure 1 and Figure 2.
Independent circuits must be designed for each of these actions.
The function-select inputs (S) determine which F is used for the
ALU output (see Table 1 and Figure 2). The carry output
should be set only when an addition causes a carry output. In
all other operations, the carry output should be false.
DEBUG OUTPUTS
It is often helpful to create extra output signals so that your circuit
design is easier to debug (in simulation and in hardware). I
suggest adding outputs for each of the functional blocks Fnot ,
(Fand , For , and Fsum). After you have thoroughly tested your
circuit through simulation, you can remove the unneeded outputs
if it is necessary to make the design fit in your PLD. But you will
NOT program this design into your PLD.
PRE-LAB REQUIREMENTS (ALU)
1. Design the ALU in Quartus (Lab4_ALU). Simulate the
circuit identifying that it works by annotating your
simulation. (Please do NOT make a simulation that includes
ALL possible input combinations.) There is NO NEED to
design an adder; just use the 74’283 described in the
Materials section of this document. Similarly, you can use
MUX’s in your design.
2. Each of the above items, including circuit schematic and
annotated Quartus simulation results should be part of the
Canvas-submitted lab document. (Of course, you should
also submit your archive file.)
3. You do NOT need to build this circuit.
PRE-LAB QUESTIONS (ALU)
1. If you were to make a complete (un-abbreviated) truth
table for your ALU, how many rows would it need? (The
answer should tell you why I did not want a simulation
including ALL input combinations.)
2. What changes would be necessary to the design already
made if you wanted to add two more functions,
F=A NOR B and F=A XOR B, where XOR is exclusiveor?
Figure 2: Function selection of ALU.
2
00 01 10 11
F
4
S MUX
4
Fsum
4
Fnot
4
Fand
4
For
S1:S0 Action Equation
00 complement of A F = /A
10 bit-wise AND F = A and B
11 bit-wise OR F= A or B
01 Sum F = A + B + Cin , Cout
Table 1. ALU functions.
 Figure 1: ALU functional block diagrams (with all
signals active-high).
ALU
Cin B A
S
4 4
2
Cout F
4
2
F 4
S
ALU
4 A
4 B
Cin
Cout
University of Florida EEL 3701 — Fall 2019 Dr. Eric M. Schwartz
Department of Electrical & Computer Engineering Revision 0 30-Sep-19
Page 2/5 LAB 4: ALU and CPU
CPU WITH RALU
A block diagram of the CPU you will design is shown in
Figure 3.
1. The device has one 4-bit wide INPUT bus and one 4-bit
wide OUTPUT bus. These buses are used to bring data to
and from the ALU. The OUTPUT bus is fed back for
possible re-entry to the system.
2. REG A and REG B are 4-bit wide registers (i.e., four D
Flip-Flops) that are used to hold data originating from
MUX A and MUX B. MUX A and B (each containing
four 4-input multiplexers) are used to connect a particular
bus to REG A and REG B, respectively. The busses are
connected to REG A and REG B as described in Table 2.
The outputs of REGA and REGB are thus fed back to
MUX A and MUX B inputs as well as to a combinatorial
logic block. The signals REGA and REGB are system
outputs.
The combinatorial logic block is used to perform data
complement, addition, ORing, ANDing, and shifts.
3. MUX C consists of four 8-input multiplexers. They are
used to select a particular operation for outputs. The three
select lines MSC2:0 function as shown in Table 3 (where
the most significant bit is on the left).
4. The carry output, Cout, should come directly from the
adder circuit (with no additional circuit necessary).
COMPILATION AND SIMULATION
In this lab, your signals REGA and REGB are required outputs
of the circuit, since these are the actual system outputs. It is
often helpful to create extra output signals (as discussed below,
called debug outputs) so that your circuit design is easier to
debug (in simulation and in hardware). For example, you
might want to output the signals that come out of MUX A and
MUX B. With these extra outputs, your design might not fit
in your PLD. In this case, you have two choices, the best of
which is to use a functional compilation and simulation (as
described in the Quartus tutorial). Using a functional
compilation and simulation will also execute much faster in
Quartus. A functional compilation and simulation is
independent of the chip chosen. I usually start all my designs
(when possible) by functional compiling my circuits before I
even attempt to fit the design onto a particular chip (full
compilation). Note that with your MAX 10 part, Quartus does
NOT have a non-functional compilation and simulation
(called a full compilation and timing simulation) available! An
alternative is to choose a bigger device (like the
10M50SCE144I7G device in the same MAX 10 family as our
10M02SCU169C8G PLD).
After you have thoroughly tested your circuit through
functional or full simulation, you can remove the unneeded
outputs, if necessary, to make the design fit into your PLD.
Functional Compilation and Simulation
When designing something this big, it is a good idea to keep a
lot of data available for simulation. Then, when you know that
your design simulates correctly, you can remove as many
outputs as needed to get the design to fit into your particular
device. Extra signals can be output and used in your
simulation. I call these extra outputs debug outputs.
A functional compilation and simulation has (effectively) no
limit on the number of inputs, outputs and internal elements
available. For a functional compilation, just select the arrow
next to “Analysis & Synthesis” in the “Compile Design” task.
Note that with your MAX 10 part, Quartus does NOT have a
non-functional compilation and simulation (called a full
compilation and timing simulation) available!
Table 3: ALU function selection MUX (for MUX C).
MSC2:0 Action
000 REGA Bus to OUTPUT Bus
001 REGB Bus to OUTPUT Bus
010 complement of REGA Bus to OUTPUT Bus
011 bit wise AND REGA/REGB Bus to OUTPUT Bus
100 bit wise OR REGA/REGB Bus to OUTPUT Bus
101 sum of REGA Bus & REGB Bus to OUTPUT Bus
110 shift REGA Bus left one bit to OUTPUT Bus
111
shift REGA Bus right one bit to OUTPUT Bus
without sign extension
Table 2: Input source MUXs for Registers A and B.
MSA1/
MSB1
MSA0/
MSB0
Bus Selected as Input
to REGA/REGB
0 0 INPUT Bus
0 1 REGA Bus
1 0 REGB Bus
1 1 OUTPUT Bus
3
4 4
4 4
REG A REG B
MUX A’s MUX B’s
MUX C’s OUTPUT Bus
REGA Bus
REGB Bus
OUTPUT Bus
MSA1
MSA0
CLK
MSC2:0
CLK
MSB1
MSB0
Combinatorial Logic
REGA Bus REGB Bus
Cin Cout
INPUT Bus
4 4
4
4
4
Figure 3: A simple CPU.
University of Florida EEL 3701 — Fall 2019 Dr. Eric M. Schwartz
Department of Electrical & Computer Engineering Revision 0 30-Sep-19
Page 3/5 LAB 4: ALU and CPU
See the section titled “E. Functional and Timing Simulation”
in your Quartus Tutorial for more information on how to
obtain a functional simulation in Quartus.
CONTROL WORD
A control word (in this case the word is 7-bits) can now be
defined as the bit pattern:
MSA1:0, MSB1:0, MSC2:0
By setting the appropriate control word bit pattern, it is now
possible to load data into the system and perform all the ALU
functions mentioned in the Objectives.
PRE-LAB REQUIREMENTS (CPU WITH RALU)
1) Draw a complete and detailed functional block diagram
(expanding on the one given above), labeling all inputs and
outputs and internal signals.
2) Design the required circuit (all call it Lab4_CPU) using
Quartus’ schematic entry (.bdf file). The signal names
should match those of your functional block diagram. In
addition to the output bus, the outputs of registers A and B
should be outputs of your design.
3) Simulate each of the simple functions (in Table 3)
implemented directly with MUX C using the Quartus
simulator. Include each of these simulations in your lab
document. (As usual, all pre-lab material must be
submitted through Canvas prior to the start of your lab. Be
sure to also submit your archive files.)
4) Derive and test control words (i.e., write and simulate
programs) to do each of the following complex functions.
Create (and turn in) a table (see Table 4) with columns
labeled CLK, MSA, MSB, MSC, etc. and showing the
sequences of steps necessary to implement each of these
complex functions. Describe what is occurring for each
line in the column labeled Description. Include these tables
in your lab document. You must save the simulation
outputs for these complex functions and include them in
your Quartus archive file. Save each simulation in a
separate file. Annotate each simulation. At a minimum,
describe in your annotation what is happening at each
active clock edge.
a) Load register A with data, complement the A data and
then store it into B. Preserve the data in A during this
operation.
b) Load A and B with known values, bit wise AND the
registers and then store the result in A. Preserve the
contents of register B during this operation.
c) Load A and B with known values, bit wise OR the
registers and then store the result in B. Preserve the
contents of register A during this operation.
d) Load A and B with known values, sum them and then
store the result in A. Preserve B during this
operation.
e) Load A with a value, shift it left one bit and then store
it in B.
f) Now write a program to ADD 3 and 7, OR the result
with 4, divide the result by 4, complement this new
result, AND the result with 3, and then finally
multiply it by 2. (Don’t worry if the result makes no
sense; just perform the required operations. This
“program” should work, independent of the inputs,
i.e., the “program” should remain unchanged even if
the 3 and 7 inputs are changed to $B and 6.)
5) Use the debounced switch (made in the previous lab) for
your clock input. If you removed this design from your
breadboard, re-build it in a corner of your breadboard and
leave it there for the remaining labs this semester.
6) Download your design to your PLD PCB with nothing else
connected to the board (except power and ground).
7) Use your DAD for inputs and you DIP LEDs (and/or 7-
segment displays) for outputs (i.e., Cout and the three
busses RegA, RegB, and Output). For testing at home, you
can use the static I/O of the DAD for the inputs. I suggest
that you start with DAD/NAD Static I/O but use a
debounced circuit for the clock input so that you can
control when the signals change. But once you are
convinced that it works okay, then you must make a DAD
custom pattern (see the bottom of page 4 in the
Waveforms Tutorial) with a single control word for each
line of Table 4 to replace your debounced circuit clock and
DAD/NAD Static I/O. You MUST use a custom pattern at
a slow enough frequency (e.g., 0.5 Hz) to see all the
number on the LEDs on the breadboard (and/or 7-segment
displays on the PLD PCB). Note that when the static I/O is
open and running, if the signals are set for buttons or
switches, the static I/O will override the pattern generator.
(If the DAD/NAD had more digital I/O pins, we could use
it for both the inputs and outputs.) Verify that your circuit
design functions as specified in the Pre-Lab Requirements,
specifically part f.
a) Save and submit the control word custom pattern file
(Lab4_4f.dwf3work) to Canvas.
b) You will demo your lab to your TA using this custom
patter file.
8) You must adhere to the Lab Rules and Policies document
for every lab. Re-read, if necessary. Documents must be
submitted through Canvas and on paper for every lab. All
pre-lab material is to be submitted BEFORE the beginning
of your lab.
IN-LAB REQUIREMENTS (CPU with RALU)
Demonstrate that part 4f works properly on CPU design on your
breadboard. Use the DAD/NAD pattern generator file
Lab4_4f.dwf3work.
PRE-LAB QUESTIONS (CPU WITH RALU)
1) Draw the single simple device that can be added to your
circuit design to “remember” the last carry output. Specify
the inputs and outputs for this device. 
University of Florida EEL 3701 — Fall 2019 Dr. Eric M. Schwartz
Department of Electrical & Computer Engineering Revision 0 30-Sep-19
Page 4/5 LAB 4: ALU and CPU
2) Will a divide by two work for all 4-bit 2’s complement
numbers? Explain.
3) Describe how you can take the 2’s complement of a
number, i.e., if A is loaded with a number, get the 2’s
complement of A into B.
4) Describe how you subtract with your CPU. Hint: See
above question.
5) Suppose you’re not allowed to use a flip-flop that has an
asynchronous CLR or SET, how can you add a function
that clears the contents of either A or B? 
University of Florida EEL 3701 — Fall 2019 Dr. Eric M. Schwartz
Department of Electrical & Computer Engineering Revision 0 30-Sep-19
Page 5/5 LAB 4: ALU and CPU
Table 4: Sample table for Pre-lab Requirement 4.
MSA MSB MSC Input Cin RegA RegB Output RegA+ RegB+ Output+ Cout+ Description
Note that the + means “after the clock edge”