# EET 1131 Unit 3

Electronics - Devices

Nov 26, 2013 (4 years and 5 months ago)

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Floyd, Digital Fundamentals, 10
th

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EET

1131 Unit 3

Basic Logic Gates

Kleitz
, Chapter 3.

Homework
#3 and Lab #3 due next
week.

Quiz next week.

Floyd, Digital Fundamentals, 10
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The inverter performs the Boolean
NOT

operation. When the
input is
LOW (0),
the output is
HIGH (1);
when the input is
HIGH, the output is LOW.

The Inverter

A

X

Input
A
X
Output

0 1

1 0

The
NOT
operation (complement) is shown with an overbar.
Thus, the Boolean expression for an inverter is
X

=

A
.

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The Inverter

Example waveforms:

A

X

A

X

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The
AND gate

produces a HIGH output when all inputs are
HIGH; otherwise, the output is LOW. For a 2
-
input gate,
the truth table is

The AND Gate

The
AND
operation is usually shown with a dot between the
variables but it may be implied (no dot). Thus, the AND
operation is written as
X

=
A
.
B
or
X = AB.

Inputs
A B
X
Output
0 0

0 1

1 0

1 1

0

0

0

1

A

B

X

&
A

B

X

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Example waveforms:

A

X

The AND Gate

A

B

X

B

&
A

B

X

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The AND Gate

A Multisim circuit is shown. XWG1 is a word generator set in
the count down mode. XLA1 is a logic analyzer with the
output of the AND gate connected to first (upper) line of the
analyzer. What signal do you expect to on this line?

The output (line 1) will be
HIGH only when all of the
inputs are HIGH.

Floyd, Digital Fundamentals, 10
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The
OR gate

produces a HIGH output if any input is HIGH;
if all inputs are LOW, the output is LOW. For a 2
-
input gate,
the truth table is

The OR Gate

The
OR
operation is shown with a plus sign (+) between the
variables. Thus, the OR operation is written as
X

=
A
+
B.

Inputs
A B
X
Output
0 0

0 1

1 0

1 1

0

1

1

1

A

B

X

A

B

X

1

Floyd, Digital Fundamentals, 10
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Example waveforms:

A

X

The OR Gate

B

A

B

X

A

B

X

1

Floyd, Digital Fundamentals, 10
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The OR Gate

A Multisim circuit is shown. XWG1 is a word generator set
to count down. XLA1 is a logic analyzer with the output

The output (line 1) will be
HIGH if any input is HIGH;
otherwise it will be LOW.

connected to first (top) line of the analyzer. The three 2
-
input OR gates act
as a single 4
-
input gate. What signal do you expect on the output line?

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The
NAND gate

produces a LOW output when all inputs
are HIGH; otherwise, the output is HIGH. For a 2
-
input
gate, the truth table is

The NAND Gate

Inputs
A B
X
Output
0 0

0 1

1 0

1 1

1

1

1

0

A

B

X

A

B

X

&
The
NAND
operation is shown with a dot between the
variables and an overbar covering them. Thus, the NAND
operation is written as
X

=
A
.
B
(Alternatively,
X = AB.)

Floyd, Digital Fundamentals, 10
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Example waveforms:

A

X

The NAND gate is particularly useful because it is a
“universal” gate

all other basic gates can be constructed
from NAND gates.

The NAND Gate

B

A

B

X

A

B

X

&

Floyd, Digital Fundamentals, 10
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The NAND Gate

A Multisim circuit is shown. XWG1 is a word generator set in
the count up mode. A four
-
channel oscilloscope monitors the
inputs and output. What output signal do you expect to see?

The output (channel D) will be
LOW only when all of the
inputs are HIGH.

Inputs

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The
NOR gate

produces a LOW output if any input is
HIGH; if all inputs are LOW, the output is HIGH. For a
2
-
input gate, the truth table is

The NOR Gate

Inputs
A B
X
Output
0 0

0 1

1 0

1 1

1

0

0

0

A

B

X

A

B

X

1
The
NOR
operation is shown with a plus sign (+) between
the variables and an overbar covering them. Thus, the NOR
operation is written as
X

=
A
+
B.

Floyd, Digital Fundamentals, 10
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Example waveforms:

A

X

The NOR operation will produce a LOW if any input is HIGH.

The NOR Gate

B

A

B

X

A

B

X

1
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Enable/Disable Using AND Gate

14

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Enable/Disable Using OR Gate

15

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Integrated Circuits

Plastic
case
Pins
Chip
Cutaway view of DIP (
D
ual
-
I
n
-
line
P
ackage)
chip:

The TTL series, available as DIPs are popular
for laboratory experiments with logic.

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Integrated Circuits

DIP chips and surface mount chips

Pin 1

Dual in
-
line package Small outline IC (SOIC)

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Integrated Circuits

Chip Densities:

Small scale integration (SSI): <=10 gates per chip.

Medium
-
scale integration (MSI): 10 to 100 gates per
chip.

Large
-
scale integration (LSI): 100 to 10,000 gates per
chip.

Very large
-
scale integration (VLSI): 10,000 to 100,000
gates per chip.

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Programmable Logic

Programmable logic devices (PLDs) are an alternative to
fixed function devices. The logic can be programmed for a
specific purpose. In general, they cost less and use less
board space than fixed function devices.

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Some common gate configurations are shown.

Fixed Function Logic

14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'
00
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'
04
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'
08
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'
02
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'
10
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'1
1
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'20
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'21
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'27
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'32
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'86
14
1
8
7
9
6
10
5
11
4
12
3
13
2
V
CC
GND
'30
Floyd, Digital Fundamentals, 10
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Website for Datasheets

Many websites have datasheets for
logic chips.

The best site is Texas Instruments:
www.ti.com

Type the chip number

(such as 7404)
i
n the Search box.

For some chips, the original part number is
obsolete and no longer available. In such
cases, inserting
LS

often works. Example:
74LS10.

Floyd, Digital Fundamentals, 10
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Troubleshooting

means finding and fixing faults in a circuit
or system that’s not working correctly.

step in troubleshooting a digital circuit on the
should always be to
verify that the voltage at
each chip’s power and ground pins are actually +5 V and 0V.

After that, use your knowledge of truth tables to find the
gates that are not producing the correct outputs.

Troubleshooting

Multisim

lets you insert the following kinds of faults into
digital components:

An open pin

Two pins shorted together

A pin shorted to
V
CC

(constant HIGH)

A pin shorted to ground (constant LOW)

Multisim

troubleshooting problems that
I’ll assign on some
homeworks