Chapter 3 (part 2)
description
Transcript of Chapter 3 (part 2)
Chapter 3 (part 2)
Basic Logic Gates
11
3-7 The Inverter
• Used to complement (invert) a digital signal– When A = 1, X = 0
– When A = 0, X = 1
• Timing analysis
2
Truth table and Boolean equations for the Inverter
• Truth Table • Boolean Equation:
X = A• Inversion bar
– Used to signify the complement
• Inverter is also called as NOT gate
3
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
4
I/O of a 7400 quad NAND IC
5
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
6
Symbols for three- and eight-input NAND gates
7
8
9
10
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
11
I/O of a 7402 quad NOR IC
12
Truth Table and Boolean equation for The NOR Gate
• Truth Table• Boolean Equation: X = A + B
13
14
15
16
3-10 Logic Gate Waveform Generation
A popular generalPurpose Repetitive waveform generator
17
Figure 3.44 Generating a 3-ms HIGH pulse using an AND gate and a Johnson shift counter.
18
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?
19
Example 3-14 Which Johnson counter outputs must be connect to a three-input AND gate to enable just the Cp#4 pulse only to be output?
20
Example 3-15 Sketch the output waveform resulting from inputting the Johnson counter outputs shown:
21
22
23
24
25
Figure 3.60 7404 TTL and 4049 CMOS inverter pin configurations.
26
Figure 3.61 (a) 7402 TTL NOR and 4001 CMOS NOR pin configurations; (b) 7400 TTL NAND and 4011 CMOS NAND pin configurations.
27
28
3-12 IEEE/IEC Standard Logic Symbols
29
30
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.
31
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.
32
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.
33
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.
4034