Logic Gates How Boolean logic is implemented. Transistors used as switches to implement Boolean...
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Transcript of Logic Gates How Boolean logic is implemented. Transistors used as switches to implement Boolean...
Logic GatesHow Boolean logic is implemented
• Transistors used as switches to implement Boolean logic:
AND OR
Logic with Transistors
Logic Gates
• Digital electronics : design of binary systems• Gates are basic building block:– One for each of 6 Boolean logic rules
at tip means NOT
Not
Plus one additional gate• NOT gate reverses a signal
Input Output
0 1
1 0
Combinations
• Output of one gate can serve as the input to the next gate
• Use to produce new logic:– Ex: Two ANDs used to make a 3 input AND
Interactive
Combinations
• Can also create basic gates from other ones• Ex: AND fed into NOT same as NAND
• NOR and NAND gates are universal– Can be used to make any other gate
• Ex: AND made with NORs:
Interactive
Universal Gates
• NOR gates can be single transistor– Electrically simple to design– Apollo’s mission computer was built
exclusively from NOR gates
NOR
Universal Gates
Useful Circuits:
• Simple Memory• Decoder• HalfAdder
Building A Truth Table
• Inputs are always the same (need every combo)– You figure out outputs:
• More inputs = more combinations 3inputs = 8 rows4 inputs = 16 rowsetc…
Input0 Input1 Output00 0 ?0 1 ?1 0 ?1 1 ?
Using the Circuit Simulator
• Always start with DC power• Use Toggles as inputs– Click name below components to rename
• Use LEDs as outputs• Wire by dragging from one
connector dot to another
Off On
Using the Circuit Simulator
• Red connector dots have power, black do not– Top input has power at
output– Bottom input is not letting
power through
• Toggle switches are “On” when light part is at bottom: