CS计算机代考程序代写 Abstraction & Digital Logic: From Transistors to Gates

Abstraction & Digital Logic: From Transistors to Gates

Wave Diagram concept
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Building functions from logic gates
 Combinational Logic Circuit
 Output depends only on the current inputs  Stateless (memoryless)
 Sequential Logic Circuit
 Output depends on the sequence of inputs (past
and present)
 Stores information (state) from past inputs
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Sequential Circuits and Memory

Combinational vs. Sequential
■ Combinational circuit
◆ Always gives the same output for a given set of
■ Sequential circuit
◆ Remembers previous input
◆ Output depends on state and input
inputs
◆ Example: Adder always generates sum and carry, regardless of previous inputs
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Sequential Circuits
■ Store information
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Reset-Set (RS) Latch – NAND SR Latch
■ Two inputs: Set and Reset
■ Setto0oneofthetwoinputsatatimetostore
a value, S sets, R clears
■ The transition to 00 generates an undefined output
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NAND SR Latch
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R-S Latch Nor Gates
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NAND SR Latch wave diagram
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NOR SR Latch wave diagram
Make up your own examples and practice!
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D Latch
E/cl D k
0 0 0 1 1
1
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S’
1
R’
R’
S’
Q
Q’ Comment
Keep state Keep state D=Q D=Q
0 1
11 11 01 10
Q Q’ Q Q’
1 0
0 1
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D Latch Wave diagram
E/cl D k
0 0 0 1
Q Q’
Keep state Keep state D D’
D D’
1
0
1
1
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D Flip Flop
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D FF positive edge wave
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