Experiment Number: 12B
Discovering Chip Configurations – 74 LS Series Continued
Purpose: To investigate the properties of various logic gates and discover the configurations
of some of the TTL chips in the 74xx LS Series.
Materials:
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Solderless breadboard – 1
Battery holder with 4 AA cells – 1
DIP switch – 1
Light Emitting Diode – 1
 470 Ω resistor – 1
 Assorted wire
 Integrated Circuits
o 7402 – 1
Set-up:
Note that the mystery gate showing is indicated by a pentagon shape.
ATTENTION: The pin configuration is DIFFERENT than before.
 With this chip, pins 2 & 3, 5 & 6, 8 & 9, 11 & 12 are the inputs.
 Pins 1, 4, 10 and 13 provide the outputs.
 Pin 7 is still ground
 Pin 14 is still connected to +6 volts
Procedure:
1. Following the schematic diagram, create a circuit according to the schematic diagram,
noting the following:
a. The resistor is 470 ohms and placed in the circuit in order to control current to the
LED.
b. The chip to put in should be the 7402.
c. DIP switches need to be toggled to closed. At this state, input A and B are both
set to low voltage or 0.
2. Complete the observation table below by recording the state of the LED (on or off) for
each combination of inputs. These can be set by toggling the switches on the DIP
switch.
Chip
Identification
7402
Input Combinations
(off – low / on - high)
A
B
off – low
off – low
off – low
on - high
on - high
off – low
on - high
on - high
Output LED State
(off – low / on - high)
Y
3. Once all inputs have been tested, disconnect the battery and remove the IC only.
Conclusion:
A. According to your observations, identify the logic gate by name, neatly draw its gate
schematic and provide the truth table with its equation for the chip you tested:
Chip
Identification
7402
Logic Gate
Name
Gate Schematic
Truth Table
A
B
0
0
1
1
0
1
0
1
Y=
B. Describe in words the behaviour of the gate you explored. Try to compose one to two
sentences. Particularly make note of when the output is high or low voltage. As well,
you might mention its behaviour in relation to another gate.
The
Gate
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C. Provide a scenario where the logic reflected in this gate’s behaviour plays out in real life.
Gate: _____________________
Real Life Scenario:
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