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Microprocessors Programming and
Interfacing
ES C 263
Basic digital devices
Murti KCS
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Objective
Review digital electronics needed for MPhardware design.
Scope
Gates
Tri-state logic
Open collector
Fan out
Multiplexers/demultiplexers
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+5
V
5
1 0 1
Time
+5
V
5
Time
Analog and Digital..
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Binary Logic
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Binary variables
Binary valuesHigh and Low
True and False
1 and 0
Yes or No
Basic binaryoperations
AND
OR
NOT
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Register
1 1X
1
0
1
1
1X
0X
1X
1X
Z=11
MSB
LSB
Z11 XX11
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AND
x y z
0 0 0
0 1 0
1 0 0
1 1 1
Z=x.y
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And as gate
1
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Masking
0 0 1 1 1 1 0 0
0 1 1 0 1 0 1 1
0 0 1 0 1 0 0 0
0 0 1 0 0
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NAND
x y z
0 0 1
0 1 1
1 0 1
1 1 0
YXZ .!
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OR
x y z
0 0 0
0 1 1
1 0 1
1 1 1
Z=x+y
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Concatenate data
0 0 1 1
1 0 1 1
0 0 0 0
0 0 0 0
1 0 1 10 0 1 1
1 0 1 1
0 0 1 1
0 0 1 1 1 01 1
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XOR
x y z
0 0 0
0 1 1
1 0 1
1 1 0
YY ..
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Comparator
Comparator
1 0 1 1
0 0 1 1
1 0 0 0
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Inverter
x z
0 1
1 0
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An inverter circuit
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TTL gate
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Inverter
Ones
Complement
01001011 10110100
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Timing diagram
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NAND implementation
F=AB+CD
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Wired logic
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Wired AND
F=(AB+CD)
AND or Invert gateAB CD F
11 X 0
X 11 0
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Open collector
Physical connection
Wired
AND logic
Opencollector gates
forming a bus
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Three-state gate
ENB
X XY Y
ENB X Y
0 X High
imp (Z)
1 0 0
1 1 1
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Tristate bus
Active low Activehigh
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Fan out
IOH=High level output current
(max)
IIH=high level input current
IOH
= 400QA
IIH
= 40QA
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Fan out..
IOL=Low level output current
(max)
IIL=Low level input current
IOL = -16QAIIL
= -1.6QA
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Fan out
)fanoutoutputLLogicfanout,outputHLogicmax(
,max_
!
!
IL
OL
IH
OH
I
I
I
IoutFan
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Fan out..
This means that each gate can drive 10 other gates in thesame
family without getting out of its guaranteed range ofoperation.
In cases where more than 10 gates are connected to theoutput of
a single gate of this family, the output voltage
levels will degrade and the gate will slow down.
Modern MOS logic families have a fan-out of about 50,since each
gate must source or sink a current only duringthe transition from H
to L or L to H.
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Multiplexer (2 to 1 line)
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Multiplexer (4 to 1 line)
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Multiplexer (8 to 1)
Note the
Enableinput
This isActiveLow
Output
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De-multiplexer
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1 to 8 de multiplexer
