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State Machines

State Machines. Another look at D latch/flip-flop. This is an example of a state diagram more specifically a Moore machine. q new = D. Synchronous state machines. If a system can both process and store information, then the values stored in the memory elements depend on both the

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State Machines

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  1. State Machines

  2. Another look at D latch/flip-flop This is an example of a state diagram more specifically a Moore machine qnew = D University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 2

  3. Synchronous state machines If a system can both process and store information, then the values stored in the memory elements depend on both the inputs and the previous values in these elements. This is called a sequential system. Such a system is also called a finite-state machine (FSM). If all changes to memory values happen at the same time as determined by a global system clock, we have a synchronous FSM. University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 3

  4. FSM definition • An FSM has the following components: • A set of states • A set of inputs • A set of outputs • A state-transition function (of the states and inputs) • An output function (of the states and maybe inputs) • Moore machine - function of states only • Mealy machine - function of states and inputs • This can be represented by a state diagram • States are circles • Arcs show the state transition function • Arcs are labeled with input values • Outputs are labels on states (Moore) or arcs (Mealy) University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 4

  5. Another example - 2-bit counter Counter starts at 0 (green) and increments each time the clock cycles, until it gets to 3 and then overflows back to 0. Only input is the clock, we don’t show that. University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 5

  6. 2-bit counter Lnew = Hold’Lold’ + HoldLold’ = Lold’ Hnew = Hold’Lold + HoldLold’ University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 6

  7. 2-bit counter with reset Lnew = R’Hold’Lold’ + R’HoldLold’ = R’Lold’ = (R + Lold)’ Hnew = R’Hold’Lold + R’HoldLold’ = R’(Hold’Lold + HoldLold’) University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 7

  8. 2-bit counter with reset University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 8

  9. Counter with 7-segment display Each segment in the display can be lit independently to allow all 10 decimal digits to be displayed (also hex) 2-bit counter will need to display digits 0-3, so will output a 1 for each segment to be lit for a given state University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 9

  10. Counter with output functions A = D = R’Ho’Lo’+R’HoLo’+R’HoLo = R’(Ho’Lo)’ B = R’ C = R’(HoLo’)’ E = R’Lo’ F = R’Ho’Lo’ = (R+Ho+Lo)’ G = R’Ho University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 10

  11. 7-segment output logic University of Texas at Austin CS310 - Computer Organization Spring 2009 Don Fussell 11

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