State
Machines
Module 11
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Reading Assignment: Sec. 5-4, 5-5, 5-6: pp. 223-247 |
Problems 1, 3, 4 |
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System state is
stored using memory elements such as latches or flip-flops
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State is updated
synchronously or asynchronously
o
Synchronously : a
discrete points in time determined by the a periodic signal such as the clock
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Asynchronously :
may be at any instant in time
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Update is
realized using combinational logic
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Output function
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Next state
function
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Outputs are
computed as a function of
§
§
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We will be only
concerned with synchronous state machines
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Example: counters
State Machine Diagrams
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Representation
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States and
transitions between states (arcs)
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Label the states
with the encoded state number
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Label the arcs
with inputs and outputs
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For Moore
machines, label the state with the output values
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A sequential circuit
can be in only one state at any given time
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We will assume
the state elements are registers
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A state
transition occurs on a clock edge
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Examples
State Transition Tables
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Inputs
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External input
signal values
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Current state
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Outputs
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Output signal
values (none for a Moore Machine)
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Next state
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Examples
Design
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Generate a
Boolean function for each external output bit
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Inputs are
external input signal values and the current state bits
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Generate a
Boolean function for each (next) state bit
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Inputs are
external input signal values and the current state bits
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Use any design
approach, for example, Boolean algebra or Karnaugh
maps.
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Implement the
Boolean expressions using mixed logic
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Examples