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Digital Circuits - Finite State Machines
We are aware that for each positive or negative transition of the
clock signal, synchronous sequential circuits suffer state changes
dependent on the input
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A
synchronous sequential circuit is sometimes referred to as a
finite state machine if it has a limited number of states
(FSMFSM)
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Mealy State Machine
Moore State Machine

Now, let us discuss about these two state machines one by one
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The block diagram of Mealy state machine is shown in the
following figure
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Memory and combinatorial logic are those
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As a result, based on the inputs and states that are now active,
the Mealy state machine produces outputs
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The state diagram of Mealy state machine is shown in the
following figure
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The
circles have these states' names inside of them, and each circle
represents a different state
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Here, input/output is
represented by the values 0/0, 1/0, and 1/1
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In general, the Mealy state machine's state requirement is lower
or equivalent to the Moore state machine's state requirement
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Moore State Machine
A Finite State Machine is said to be Moore state machine, if
outputs depend only on present states
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The Moore state machine has two pieces, as depicted in the
picture
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The
following states in this scenario are determined by the current
inputs and states
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As a
result, the outputs won't be valid until the state changes
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In the above figure, there are four states, namely A, B, C & D
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Here, only the input value is labeled on each transition
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The number of states needed for the Moore state machine is
typically greater than or equal to the number needed for the
Mealy state machine
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Therefore, depending on the
need, we can use one of them
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These are control circuits and digital circuits with data paths
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Conversely, control circuits dictate how digital circuits
operate
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Algorithmic State Machine ASMASM charts
can be used to get around this problem
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They are utilized to depict the
progression of operations that will be carried out by control and
data path circuits
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State box
• Decision box
• Conditional output box
State box
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State box is represented in rectangular shape
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The symbol of
state box is shown in the following figure
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Name of the state
is placed to the left of state box
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Moore state machine outputs can also be placed inside
state box
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The symbol of
decision box is shown in the following figure
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The inputs or
Boolean expressions can be placed inside the decision box,
which are to be checked whether they are true or false
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Otherwise, it will
prefer path2
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The symbol of conditional output box is shown in the following
figure
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The conditional outputs can be placed inside state box
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So, based on the requirement, we can
use the above components properly for drawing ASM charts

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