Transcript Transistors and Logic Gates

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Complete Example
A blinking traffic sign
•
•
•
•
•
No lights on
1 & 2 on
1, 2, 3, & 4 on
1, 2, 3, 4, & 5 on
(repeat as long as switch
is turned on)
3
4
1
5
2
DANGER
MOVE
RIGHT
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Traffic Sign State Diagram
Switch on
Switch off
State bit S1
State bit S0
Outputs
Transition on each clock cycle.
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Traffic Sign Truth Tables
Outputs
(depend only on state: S1S0)
Next State: S1’S0’
(depend on state and input)
Switch
Lights 1 and 2
Lights 3 and 4
Light 5
In
S1
S0 S1’ S0’
0
X
X
0
0
S1
S0
Z
Y
X
1
0
0
0
1
0
0
0
0
0
1
0
1
1
0
0
1
1
0
0
1
1
0
1
1
1
0
1
1
0
1
1
1
0
0
1
1
1
1
1
Whenever In=0, next state is 00.
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Traffic Sign Logic
Master-slave
flipflop
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Controller + Data Path
Sometimes there are lots and lots of states,
but a fairly simple way to move between states.
We can separate the data being transformed
from the state machine that's controlling the transform.
State Machine
Combinational
Logic Circuit
Storage
Elements
Controller
+
Data Path
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Controller + Data Path Example (1)
3-7
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Controller + Data Path Example (2)
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From Logic to Computer Data Path
The data path of a computer is all the logic used to
process information.
• See the data path of the LC-3 on next slide.
Combinational Logic
• Decoders -- convert instructions into control signals, access
memory
• Multiplexers – select inputs and outputs
• ALU (Arithmetic and Logic Unit) – performs operations on data
Sequential Logic
• State machine -- coordinate control signals and data movement
• Registers and latches -- storage elements
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LC-3 Data Path
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