2 basic logic gate
TRANSCRIPT
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Should be able to:
Describe the operation and use of AND andOR gates
Construct truth table for 2, 3 and 4 input ANDand OR gates
Draw timing diagrams for AND and OR gates
Describe the opration, using timing analysis, ofan enable function
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Basic Logic Gates
Objectives
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AND Gate
OR Gate Timing Analysis Enable and Disable Functions
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Outlines
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A B X
0 0 0
0 1 01 0 0
1 1 1
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Manual & Diodeswitches Truth Table
BooleanequationX = A.B
AND Gate
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Manual & Transistor switches Truth Table
BooleanequationX = A + B
A B X
0 0 0
0 1 1
1 0 1
1 1 1
OR Gate
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Number of inputs to a logic gate Number of combinations 2n
Examples forAND function
n = 2: Y = A B
n = 3: Y = A B C
n = 4: Y = A B C D
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Fan-In
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Useful for visually illustratingthe level attheoutputfor varyinginput-level changes
Timingwaveformsobservedon anoscilloscopeor a logic analysis
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Timing Analysis
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Sketch the output waveform
at X for the three-input AND
gate shown, with the given
A, B and C input waveforms
The input waveform at A
and the output waveform at
X are given for the ANDgate. Sketch the input
waveform that is required at
B to produce the output at X
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example
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AND andORgatescanbe usedtoenable/disable a waveformfrombeingtotransmittedfromonepointto another
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Enable and Disable Functions
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Using an AND gatetoenable/disable a clockoscillator Active High, 1 enable
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Using anORgatetoenable/disable a clockoscillator
Active Low, 0 enable
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1. Understand the theory and operation of the
circuit, devices and ICs
2. Use Logic Pulser and Logic Probe Logic probe state
Logic
level
Indicator
lamp
HIGH (1) On
LOW (0) Off
Float Dim
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Introduction to
Troubleshooting Techniques
Logic probe
Logic pulser
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The clock enable circuit shown in figure is not working. The
enable switch is up in the enable position. A logic probe is
placed on the following pins and gets the following results. Findthe cause of the problem.
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Probe on pin Indicator lamp Indicator lamp
1 Flashing Flashing
2 On Off
3 Off Off
7 Off Off
14 On On
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example
An OR gate can be used in all those situations where the occurrence of any one
or more than one event needs to be detected or acted upon. One such example is
an industrial plant where any one or more than one parameter exceeding a preset
limiting value should lead to initiation of some kind of protective action. Figure
below shows a typical schematic where the OR gate is used to detect either
temperature or pressure exceeding a preset threshold value and produce the
necessary command signal for the system.
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PIN Logic level
1 HIGH
2 LOW
3 LOW
4 LOW
5 LOW
6 HIGH
7 LOW
8 HIGH
9 LOW
10 LOW
11 LOW
12 LOW
13 HIGH
14 HIGH
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Power
supply
+
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The following data table was built by putting a
logic probe on every pin of the hex inverter.Are there any problems with the chip? if so,
which gate(s) are bad?
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Power
supply
Logicprobe
The logic probe is always OFF
whether the switch is in the up or
down position. Is the problem with
the inverter or the NOR, or there
is no problem?
If the logic probe come ON when
the switch is in the down position.
Further testing with the probe
shows that pins 2 and 3 of the
NOR IC are both LOW. Isanything wrong? If so where is the
fault?
quiz