Transcript Lecture Outline • • • • • Bits Gates Combinatorial Logic Spice Hands-On Stuff Definition • “Digital” comes from the Latin word for “fingers” and indicates that there are many discrete signals that.

Lecture
Outline
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Bits
Gates
Combinatorial Logic
Spice
Hands-On Stuff
Definition
• “Digital” comes from the Latin word for
“fingers” and indicates that there are
many discrete signals that are at one of
two values.
Logic Gates
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NOT
AND
NAND
OR
NOR
XOR
XNOR
Logic Inverter
NOT = “!”
OUT=!A
A fictional AND Circuit
The light bulb only turns on when
both A and B are closed.
Truth Table
AND = “&”
OUT=A & B
NAND
OUT=!(A&B)
A fictional OR Gate
The light bulb turns on when either A or B is closed
An OR GATE
OR = “+”
OUT=A+B
A NOR Gate
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OUT=!(A+B)
XOR Gate
• XOR=Exclusive OR
–XOR returns a True output if only one
of its input is true
XOR=A ^ B
XNOR
Combinatorial Circuits
Logic Expresions
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1=A&B
2=!(A+C)
3=!2
4=1&3
5=B&2
Output=4 ^ 5
Multisim Example
CMOS VS. TTL
CMOS
TTL
Various Logic Gates
Exercise
• Setup:
– Pin 1: 4.8 V
– Pin 2: 1.3 V-5 V
– Pin 14: 4.8 V
– Pin 7: GND
• Problem:
– Pin 3: 0.18 V (?)
NAND Characterization