1. Chapter 3 Basic Logic Gates
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2. The AND Gate
The output, X, is HIGH if input A AND input B are both HIGH
See Figure 3-1
Truth Table - see Table 3-1
Boolean Equation X = A and B or X = AB
Can have more than two inputs
Number of combinations = 2N
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3. Figure 3-1
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5. The OR Gate
The output at X will be HIGH whenever input A OR input B is HIGH or both are HIGH
See Figure 3-5
Truth Table - see Table 3-3
Boolean Equation X = A + B
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6. Figure 3-5
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8. Timing Analysis Timing Diagram Oscilloscope Logic Analyzer
voltage versus time
up to two
Logic Analyzer
state table
up to 16
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9. Enable and Disable Functions
turn ON
see Figure 3-17
Disable
turn OFF
see Figure 3-18
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10. Figure 3-18
Figure 3-17
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11. Using Integrated Circuit Logic Gates
See Figure 3-20
Enable and Disable
Pin Connections
VCC and GND
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12. Figure 3-20
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13. Introduction to Troubleshooting Techniques
The procedure used to find the fault or trouble in a circuit.
Logic Probe
metal tip
indicator lamp(s)
Floating - open circuit, neither HIGH nor LOW
Logic Pulser - provide digital signal to a circuit
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14. The Inverter Used to complement or invert a digital signal
See Figure 3-27
Truth Table - see Figure 3-27
Boolean Equation X = A
Inversion bar
NOT gate
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15. Figure 3-27
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16. The NAND Gate Same as the AND gate except that its output is inverted
See Figure 3-29
Truth Table - see Table 3-6
Boolean Equation X = AB
multiple inputs - the output is always HIGH unless all inputs go HIGH
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17. Figure 3-29
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19. The NOR Gate Same as the OR gate except that its output is inverted
See Figure 3-36
Truth Table - see Table 3-8
Boolean Equation X = A + B
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20. Figure 3-36
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22. Logic Gate Waveform Generation
Repetitive waveform
Waveform generator
Johnson shift counter
See Figure 3-43
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23. Figure 3-43
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24. Using Integrated-Circuit Logic Gates
Hex - six gates
Quad - four gates
Three-, four-, and eight-input configurations
See Figures 3-60 and 3-61
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25. Figure 3-61
Figure 3-60
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26. Summary of Basic Logic Gates and IEEE/IEC Standard Logic Symbols
See Table 3-9
See Figure 3-65
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28. Figure 3-65
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29. 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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30. 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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31. 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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32. 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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33. Summary
Manufacturer’s data manuals are used by the technician to find the pin configuration and operating characteristics for the ICs used in modern circuitry.
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