chapter 3 basic logic gates william kleitz digital electronics with vhdl, quartus® ii version...

Chapter 3

Basic Logic Gates

William KleitzDigital Electronics with VHDL, Quartus® II Version

Copyright ©2006 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

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




Figure 3-1




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


• Boolean Equation X = A + B




Figure 3-5




Timing Analysis

• Timing Diagram

• Oscilloscope– voltage versus time– up to two

• Logic Analyzer– state table– up to 16




Enable and Disable Functions

• Enable– turn ON– see Figure 3-17

• Disable– turn OFF– see Figure 3-18




Figure 3-17

Figure 3-18




Using Integrated Circuit Logic Gates

• See Figure 3-20

• Enable and Disable

• Pin Connections

• VCC and GND




Figure 3-20




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




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




Figure 3-27




The NAND Gate

• Same as the AND gate except that its output is inverted

• See Figure 3-29


• Boolean Equation X = AB

• multiple inputs - the output is always HIGH unless all inputs go HIGH




Figure 3-29




The NOR Gate

• Same as the OR gate except that its output is inverted

• See Figure 3-36


• Boolean Equation X = A + B




Figure 3-36




Logic Gate Waveform Generation

• Repetitive waveform

• Waveform generator– Johnson shift counter

• See Figure 3-43




Figure 3-43




Using Integrated-Circuit Logic Gates

• Hex - six gates

• Quad - four gates

• Three-, four-, and eight-input configurations

• See Figures 3-60 and 3-61




Figure 3-60

Figure 3-61




Summary of Basic Logic Gates and IEEE/IEC Standard Logic

Symbols

• See Table 3-9

• See Figure 3-65




Figure 3-65




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




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




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




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




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.




chapter 3 basic logic gates william kleitz digital electronics with vhdl, quartus® ii version...

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