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Registers; State Machines Analysis

Registers; State Machines Analysis. Section 7-1 Section 5-4. Definition. Register – a set of flip-flops May include extensive logic to control state transition register also refers to fast memory for storing data in a computer. Simple Register. Store D = (D 0 D 1 D 2 D 3 )

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Registers; State Machines Analysis

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  1. Registers; State Machines Analysis Section 7-1 Section 5-4

  2. Definition • Register – a set of flip-flops • May include extensive logic to control state transition • register also refers to fast memory for storing data in a computer

  3. Simple Register • Store D = (D0 D1 D2 D3) • On positive edge of Clock • Clear signal normally high • Power-up reset

  4. Register with Load Control • If load signal is H • D0 , D1 , D2 , D3 reach inputs of FFs • If load signal is L, Q is fed back • Q0 , Q1 , Q2 , Q3 reach inputs of FFs • FFs Keep same value

  5. State Machines: Analysis and Design • How to design machines that go through a sequence of events • Basically close this loop

  6. Analysis of Sequential Circuits • Earlier we learned how to analyze combinational circuits • Now extend to synchronous sequential • Include time • We’ll use state tables and state diagrams

  7. Input Equations: D FF Example Describe inputs to FF with logic equations

  8. Determining Next State and Output Current state= {A(t), B(t)} = values stored in FFs during clock t Next state= {A(t+1), B(t+1) = values stored in FFs during clock t+1}

  9. Determining Next State and Output The current state {A(t), B(t)} & input X are used to determine next state {A(t+1), B(t+1)}

  10. Determining Next State and Output (cont.) Current state & input X are used to determine output, Y • Synchronous circuit • State transitions are at positive edge of clock

  11. At time t+1 At time t State Table • Just truth table with state added

  12. Two Dimensional State Table • Same thing, different layout

  13. Sequential Circuit Types • Moore model – outputs depend on states • Mealy model – outputs also depend on inputs

  14. Inputs State/Output State Diagram • Alternative representation for state table • Moore: outputs depend only on states

  15. Input/Output --------------------------------------------- State Table for Circuit of Figure 5-15 Mealy Model • Output depends on input and state State Table for Circuit of Figure 6-17

  16. State Table vs. Diagram • Same information • Table is perhaps easier to fill in from description • Diagram is easier for understanding and writing code • You can label states with English description

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