270L13-Sequential+Blocks

270L13-Sequential+Blocks - Sequential Blocks Goal is to...

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1 1 UM EECS 270 Fall 2009 Sequential Blocks • Goal is to create a toolbox of frequently used sequential devices –Reg is te rs – Counters • Ripple counter • Parallel counter – Shift Registers • Parallel in shift register • Universal shift register – Shift Register Counters • Ring counter • Johnson counter • Linear feedback shift register 2 Registers A collection of two or more D flip-flops with a common clock is called a register Used to store a collection of bits D Q QB D Q QB D Q QB D Q QB CLK Q0 Q1 Q2 Q3 D1 D0 D2 D3 Adding a mux at the input of each D FF allows for loading new value or storing current value D Q QB D Q QB D Q QB D Q QB 1 0 1 0 1 0 1 0 EN CLK Q0 Q1 Q2 Q3 D1 D0 D3 D3
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2 3 UM EECS 270 Fall 2009 Counters Very common FSM block No physical counter can count forever – real counters are modulo counters – I.e., they “count” through a finite number of states and then repeat – The number of states in a counter’s sequence is called the modulus of the counter – Example: A counter that counts the sequence 0, 1, 2, …, 7, 0, 1,… is a modulo 8 counter •A ripple counter is an easy counter implementation - State changes ripple through the circuit - Outputs don’t change at the same time! What is the modulus of this counter ? 8 4 Parallel Counter Would like all state variables to run on the same clock signal Examining the binary code yields an easy implementation: - Under what condition does each bit toggle?
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This note was uploaded on 04/18/2011 for the course EECS 270 taught by Professor David during the Spring '11 term at Michigan State University.

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270L13-Sequential+Blocks - Sequential Blocks Goal is to...

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