EE 110 Lab Experiment #3 Fall 2009
NAME: ______
EXPERIMENT 4: Experimentally Verify a Boolean Theorem (1 week)
The purpose of this laboratory is to learn to use TTL circuits to implement combinational logic and to experimentally test a theorem developed in class. Students will work individually.
Background:
The following diagrams illustrate the pinouts of several TTL devices we have in stock. These integrated circuits are in Dual In-line Packages (DIP), consisting of a central case with two rows of pins. Seen from the top (i.e., the pins pointing away from you), look for the dent or notch at one end. This notch indicates the origin for pin numbering. Pins are numbered consecutively, going counterclockwise from the notch.
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 theorem: AB + AC = AB + ABC
1) In the space provided on the next page, neatly draw the logic diagram for the left-hand side of the equation: AB + AC Clearly label the three inputs A, B, and C. Label the output Y1.
2) Label each gate with the 7400 family part number you plan to use. (Example: a 2-input AND gate can be realized by choosing a 74LS08 device.)
3) Label the inputs and output of each gate with the pin numbers you wish to use for the chosen device. (Example: One of the four 2-input AND gates in the 74LS08 package could be selected. Its inputs are pins 1 and 2 and its output is pin 3.)
Figure 1: Neatly drawn logic diagram of the left side of the theorem equation
4) Now build this logic circuit on your proto board. Use 22-gauge wire to make the connections.
- Make sure power is turned off. Plug the chosen parts into your proto board in the correct places (use the area on the left side of the proto board). Wire each part to power and ground as required. (Connect to the power busses you configured in the first lab experiment. Use RED wires for your connections to the +5V supply and BLACK wires for the GND connections.)
- Connect wires as needed to make connections between gates. Use other colors besides red and black. Be sure to double check your pin numbers. It pays to be careful and meticulous!
- Connect the output to the leftmost of the 8 single LEDs above your proto board.
- Wire input A to switch SW2, input B to SW1, and input C to SW0.
5) Check your wiring. Make sure you have not connected a gate output directly to a switch. Make sure your power connections (RED) and ground connections (BLACK) are correct to each chip. Apply power and briefly test 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.
6) Assuming everything is fine, let’s design and build a second logic circuit to realize the right-hand side of the theorem equation. As before, 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. Notice that your expression requires a 3-input AND gate. You can use two 2-input AND gates from the 74LS08 package to achieve this function.
Figure 2: Neatly drawn logic diagram of the right side of the theorem equation
7) Now build this second logic circuit on your proto board.
- Make sure power is turned off. Plug in the parts on your proto board, using the next area to the right of the first circuit. Wire power and ground connections as needed, using RED and BLACK wires.
- Make inter-gate connections as required, using other color wires.
- Connect the output (Y2) to the next LED (just to the right of the one you are already using in your first logic circuit).
- 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.
8) 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.
9) Demonstrate the operation of your two logic circuits to the teaching assistant.
TA Signature: ______
10) 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 / Output Y1 / Output Y20 / 0 / 0
0 / 0 / 1
0 / 1 / 0
0 / 1 / 1
1 / 0 / 0
1 / 0 / 1
1 / 1 / 0
1 / 1 / 1
11) 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?
12) 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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