Download Lab 5

EE 110 Lab
Experiment #5
Fall 2009
NAME: _________________________________
EXPERIMENT 5: Experimentally Compare SOP and POS Forms (1 week)
The purpose of this laboratory is to experimentally test the equivalence of SOP and POS combinational
logic. Students will work individually.
Background:
The following diagrams illustrate the pinouts of several TTL devices we have in stock.
In all cases, pin 7 must connect to GND and pin 14 to the +5V power supply. Without proper power and
ground connections, the device will not function. DO NOT wire these backwards – you will destroy the part!
Procedure:
Given the Boolean expression:
_
_
f(A,B,C) = AB + AC + BC
1) In the space provided on the next page, neatly draw the logic diagram that realizes this Sum-ofProducts (SOP) expression. Clearly label the three inputs A, B, and C. Label the output Y1.
On the last page, fill in the truth table for the expected output f(A,B,C) column.
2) Label each gate with the 7400 family part number you plan to use. Label the inputs and output
of each gate with the pin numbers you wish to use for the chosen device. Note: you can realize
a 3-input OR gate using two 2-input OR gates.
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EE 110 Lab
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Fall 2009
Figure 1: Neatly drawn logic diagram that directly realizes the given SOP Boolean expression
3) Now carefully build this logic circuit on your proto board. Use 22-gauge wire to make the
connections. Check your work thoroughly before applying power to your circuitry.
a. Make sure power is turned off. Plug the chosen parts into your proto board. Wire each
part to power and ground as required. You must use RED wires for your connections
to the +5V supply and BLACK wires for the GND connections. RED and BLACK
wires must not be used for other connections! The TA or professor has the right to
remove wires that do not adhere to this convention!
b. Connect wires as needed to make connections between gates. Use other colors besides
red and black.
c. Connect the output to the leftmost of the 8 single LEDs above your proto board.
d. Wire input A to switch SW2, input B to SW1, and input C to SW0.
4) Check your wiring.
a. Make sure you have not connected a gate output directly to a switch.
b. Make sure your power connections (RED) and ground connections (BLACK) are correct
to each chip. Power should go to pin 14; GND should go to pin 7.
c. Make sure you have not connected two gate outputs together.
d. Apply power and briefly test your circuit by exercising the three switches and watching
the LED response. If the circuit doesn’t work correctly, use the logic probe to help track
down the problem by checking each gate input and output as you manipulate the
switches.
5) Assuming everything is fine, leave that circuit in place as you design and build a second logic
circuit. This new circuit must be a Product-of-Sums (POS) equivalent to the given Boolean
expression. Use the truth table output obtained for the SOP representation of f(A,B,C) to find
the POS form. Remember that every line in the truth table where the output is low represents a
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EE 110 Lab
Experiment #5
Fall 2009
maxterm in the POS expression. You may simplify the expression obtained, if desired; however,
be certain that you are simplifying correctly. Otherwise your POS expression will not be
equivalent to your SOP expression. Choose the parts, draw the logic diagram, label the inputs
and output by name (i.e., Y2), and label all required pin numbers. Space for the logic diagram is
given on the next page.
Figure 2: Neatly drawn logic diagram that realizes the POS expression equivalent to the given expression
6) Now build this second logic circuit on your proto board. Connect the output to another LED
indicator. Wire the A, B, and C inputs to the same switches you used for the first circuit. These
switches can feed both logic circuits at the same time.
7) Carefully check your wiring. If all is good, apply power and test. You should now see the
responses of both circuits at the same time – one LED for each output. If this new circuit does
not behave properly, you’ll have to find and fix the problem. In that case, the problem may be in
either your wiring or your design.
8) Demonstrate the operation of your two logic circuits to the teaching assistant or professor. Get
their signature and comments regarding the functionality of your circuits.
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EE 110 Lab
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Fall 2009
TA Signature: _______________________________________________________________
9) Complete the following truth table according to the observed behavior of your two logic circuits.
In this table, 1 represents high voltage and 0 represents low voltage.
Input A
Input B
Input C
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
Expected
f(A,B,C)
Observed
Y1
Observed
Y2
10) Describe your results.
a. What results did you obtain in this experiment?
b. What difficulties did you have?
c. What are your conclusions? What did you learn about SOP and POS forms?
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EE 110 Lab
Experiment #5
Fall 2009
11) Once your work is complete, please dismantle your wiring and remove the chips you installed.
(Leave the power bus wiring in place.) Return your chips to the correct places in the parts bin.
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