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Introduction to Sequential Logic Design
Flip-flops
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Prev… Latches S-R S-bar-R-bar S-R with enable signal D
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FF vs. Latch Latches and flip-flops (FFs) are the basic building blocks of sequential circuits. latch: bistable memory device with level sensitive triggering (no clock), watches all of its inputs continuously and changes its outputs, independent of a clocking signal. flip-flop: bistable memory device with edge-triggering (with clock), samples its inputs, and changes its output only at times determined by a clocking signal.
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Edge triggered D Flip-Flop
A D FF combines a pair of D latches. Master/slave D FF Positive-edge-triggered D FF Negative-edge-triggered D FF
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Positive-Edge-triggered D flip-flop
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Positive-Edge-triggered D flip-flop
Dynamic-input indicator
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Edge-triggered D flip-flop behavior
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Edge-triggered D flip-flop behavior
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Edge-triggered D flip-flop behavior
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D flip-flop timing parameters
Propagation delay (from CLK) Setup time (D before CLK) Hold time (D after CLK)
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D FF with asynchronous inputs
Force the D FF to a particular state independent of the CLK and D inputs. PR (Preset) and CLR (Clear)
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Negative-edge triggered D FF
Simply inverts the clock input. Active low.
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Negative-edge triggered D FF
Simply inverts the clock input. Active low.
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J-K flip-flops Not used much anymore
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T (toggle) flip-flops A T FF changes state on every tick of the clock. (be toggled on every tick) Q has precisely half the frequency of the T. Important for counters Positive-edge-triggered T FF
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T (toggle) flip-flops with enable
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T (toggle) flip-flops with enable
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Next… FSM analysis Read Ch-7.3
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