2 basic logic gate

8/6/2019 2 Basic Logic Gate

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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

2

Outlines


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A B X

0 0 0

0 1 01 0 0

1 1 1

3

Manual & Diodeswitches Truth Table

BooleanequationX = A.B

AND Gate


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4


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5

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

+

-

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

2 basic logic gate

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