CSU22022, 9th Lecture, Dr. M. Manzke, Page: 1
The Control Unit
Control unit’s job:
Supply all the control signals to the datapath
Respond appropriately to its status signals:
Z, N, C, V
Control
Unit
Datapath
Control
Signals
Status
Signals
Data InputControl Inputs
Control Outputs Data Output
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Architecture
Input to the control unit:
A stream of instructions coming from
memory M
This steam must be converted to a
sequence of micro-operations for the
datapath
Control Unit uses:
Program counter PC to index in M the next
executable instruction
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Algorithmic State Machine
Data processing may be achieved through:
Sequencing Register transfer operations
May be specified as hardware algorithm
Consists of a finite number of procedural steps
ASM are used:
Control Unit
Datapath
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ASM Chart
Algorithmic State Machine (ASM) Chart
Defines the hardware algorithm
Defines relation ship to time
Clock
Three basic elements:
State Box
Decision Box
Conditional Output Box
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State Box
State Box contains:
Register transfer operation or output signals that are activated
while the control unit is in this state.
RUN is 1 for any box it appears and 0 for any box it does not
appear.
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Decision Box
Exit path is taken if input condition is:
True (1)
False (0)
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Conditional Output Box
Conditional Output Box entry path must pass
through one or more decision boxes.
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ASM Box Example
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ASM Block