Chapter 3 (part 2)

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Chapter 3 (part 2)

• Basic Logic Gates

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3-7 The Inverter

• Used to complement (invert) a digital signal
• When A 1, X 0
• When A 0, X 1
• Timing analysis

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Truth table and Boolean equations for the Inverter

• Boolean Equation
• X A
• Inversion bar
• Used to signify the complement
• Inverter is also called as NOT gate

• Truth Table

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3-8 The NAND Gate

• Same as the AND gate except that its output is
  inverted
• If A 1 and B 1, X 0
• If A 0 or B 0, A 1

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I/O of a 7400 quad NAND IC
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Truth table and Boolean equations for the NAND
Gate

• Boolean Equation X AB
• Multiple inputs - the output is always HIGH
  unless all inputs go HIGH

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Symbols for three- and eight-input NAND gates
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3-9 The NOR Gate

• Same as the OR gate except that its output is
  inverted
• If A 1 or B 1, X 0
• If A 0 and B 0, X 1

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I/O of a 7402 quad NOR IC
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Truth Table and Boolean equation for The NOR Gate

• Truth Table
• Boolean Equation X A B

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3-10 Logic Gate Waveform Generation
A popular general Purpose Repetitive waveform
generator
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Figure 3.44 Generating a 3-ms HIGH pulse using
an AND gate and a Johnson shift counter.
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Example 3-13 Which Johnson counter outputs will
you connect to an AND gate to get a 1ms
HIGH-level output from 4 to 5ms?
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Example 3-14 Which Johnson counter outputs must
be connect to a three-input AND gate to enable
just the Cp4 pulse only to be output?
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Example 3-15 Sketch the output waveform resulting
from inputting the Johnson counter outputs shown
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Figure 3.60 7404 TTL and 4049 CMOS inverter pin
configurations.
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Figure 3.61 (a) 7402 TTL NOR and 4001 CMOS NOR
pin configurations (b) 7400 TTL NAND and 4011
CMOS NAND pin configurations.
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3-12 IEEE/IEC Standard Logic Symbols
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Summary

• The AND gate requires that all inputs are HIGH in
  order to get a HIGH output.
• The OR gate outputs a HIGH if any of its inputs
  are HIGH.
• An effective way to measure the precise timing
  relationships of digital waveforms is with an
  oscilloscope or a logic analyzer.

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Summary

• Beside providing the basic logic functions, AND
  and OR gates can also be used to enable or
  disable a signal to pass from one point to
  another.
• There are several integrated circuits available
  in both TTL and CMOS that provide the basic logic
  functions.

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Summary

• Two important troubleshooting tools are the logic
  pulser and the logic probe. The pulser is used
  to inject pulses into a circuit under test. The
  probe reads the level at a point in a circuit to
  determine is it is HIGH, LOW, or floating.
• An inverter provides an output that is the
  complement of its input.

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Summary

• A NAND gate outputs a LOW when all of its inputs
  are HIGH.
• A NOR gate outputs a HIGH when all of its inputs
  are LOW.
• Specialized waveforms can be created by using a
  repetitive waveform generator and the basic gates.

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