lect7 Latches and flip-flops

lect7 Latches and flip-flops - CSE140: Components and...

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1 1 Sources: TSR, Katz, Boriello & Vahid CSE140: Components and Design Techniques for Digital Systems Latches and flip-flops Tajana Simunic Rosing 2 Sources: TSR, Katz, Boriello & Vahid "remember" "load" "data" "stored value" Simplest circuits with feedback
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2 3 Sources: TSR, Katz, Boriello & Vahid Bit Storage - SR Latch Q S (set) SR latch R (reset) 4 Sources: TSR, Katz, Boriello & Vahid Flight attendant call button Flight attendant call button – Press call: light turns on Stays on after button released – Press cancel: light turns off – Logic gate circuit to implement this? a a 3.2 Bit Storage Blue light Call button Cancel button 1. Call button pressed – light turns on Bit Storage Blue light Call button Cancel button 2. Call button released – light stays on Bit Storage Blue light Call button Cancel button 3. Cancel button pressed – light turns off
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3 5 Sources: TSR, Katz, Boriello & Vahid What if a kid presses both call and cancel? R S Q Call but ton Blue light Cancel but ton 6 Sources: TSR, Katz, Boriello & Vahid Reset Hold Set Set Reset Race R S Q \Q 100 SR Latch - Timing behavior R S Q Q'
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4 7 Sources: TSR, Katz, Boriello & Vahid Theoretical R-S latch state behavior R S Q Q' 8 Sources: TSR, Katz, Boriello & Vahid Q(t+ Δ ) R S Q(t) R-S latch analysis • Break feedback path R S Q Q'
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5 9 Sources: TSR, Katz, Boriello & Vahid Oscillation solution: Level-Sensitive SR Latch R1 S1 S C R Level-sensitive SR latch Q a 10 Sources: TSR, Katz, Boriello & Vahid Clocks R1 S1 S X Y C Clk R Q Level-sensitive SR latch
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6 11 Sources: TSR, Katz, Boriello & Vahid clock’ R’ and S’ changing stable changing stable stable Clocks for an SR latch clock’ S’ Q’ Q R’ R S 12 Sources: TSR, Katz, Boriello & Vahid Level-Sensitive D Latch R S D C D latch Q DQ Q C R1 S1 S X Y C Clk R Level-sensitive SR latch Q
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lect7 Latches and flip-flops - CSE140: Components and...

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