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EC262 Topic 13: Analysis and Design of Sequential SystemsI
How do we design a
combinational
system?
This approach will not work for
sequential
systems!
Why not?
So, a different approach is needed to design sequential circuits.
But…good news… we have already dealt with many of the tools involved.
We will need to use:
•
State tables: a description of how the system behaves, showing the inputs and present state, and the next
state (and possibly outputs).
•
State diagrams: each state is a vertex, and arcs indicate how the inputs drive us from one state to
another.
Think: How many states can a sequential circuit have?
The set of states corresponds to all possible values of
and so forth.
Thus, our sequential logic circuit shifts from state to state, depending on the bits held in its
memory, and the current inputs.
Note that the number of states is
finite
.
So we can imagine our sequential circuit bouncing around from state to state as time progresses.
It is common
for the sequential circuit to produce an output during each transition
Again: What causes a sequential circuit to arrive in a specific state?
•
•
Again: What does the sequential circuit do based on this?
Note that if the sequential logic circuit is in a specific state, say
X
, and then has specific inputs, say
I
, it will
always go to a next specific state as determined by its circuitry, say state
Y
.
Again, if the circuit is in state
X
and
has input
I
, it will be driven deterministically to state
Y
. It will
not
be driven to state
Y
today, but under the same
conditions to some other state, say
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This note was uploaded on 03/27/2012 for the course ECE 200 taught by Professor Nasis during the Spring '08 term at Drexel.
 Spring '08
 NASIS

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