Control Components
Introduction
We’ve looked at fundamental building blocks
That comprise the datapath in embedded design
Now want to look at control aspects
Control component typically expressed as
Finite state machine
Collection of such machines
Such devices form basis for control
Most modern computing and control systems
Fundamental Mealy and Moore models
Adequate for
Introducing FSM concepts
Expressing and implementing small designs
Expressive power limited for larger systems
Combinational explosion
When trying to develop input equations
Quickly limits utility
Will first do quick review of basic concepts
Then explore how we can put them to work
Implementation of FSM may be in hardware or software
Hardware implementation of such machines
•
LSI
•
Arrayed logic
•
PLD
•
ROM
•
Discrete logic
Earlier in our studies
We’ve looked at the basic storage element
Some simple counting and dividing circuits
Simple state machines
Like counter, divider, timer
Have
No inputs other than clock
Only primitive outputs
Such machines referred to as
autonomous clock
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We have classed such basic machines as part of datapath
In some applications can also be considered as part of control
As we move to more complex designs
Introduce
Inputs
Outputs offering rich functionality
Such functionality based upon
State of the machine
Inputs to the machine
Finite State
Machine
Outputs
Inputs
Our high level block diagram begins with following
Now we have
Set of inputs
Set of outputs
Important to recognize
Outputs may be
State variables
Combinations of state variables
Combinations of
State variables
Inputs
Let’s increase the level of detail of out state machine
We’ll reflect the
Inputs
State variables
Inputs
Outputs
Finite State
Machine
State Variables
Outputs
We see that our state variables
Fed back as inputs to our system
We’re now looking at the essence of the strength of the machine
It has the ability to
Recognize the state that it is in
Based upon the values of the state variables
React based upon that information
Decision as to which state to go to next now based upon
The current input
The state that the machine is currently in
Let’s continue increasing the level of detail
We’ll increase our view to now include
Storage elements comprising the machine
Combinational logic
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