Electronic – Active high-active low for preset

digital-logicflipflopripple-counter

In a FF when clear is 0, output is also 0.So what should it be considered as ? Active low or high clear? If it active low doesn't it mean that output should be 1 ?

Best Answer

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Preset and Clear are two asynchronous inputs in a Flip-Flop.

"Preset" is used to set its output to '1' and "Clear" is used to reset its output to '0'.

Active-low Preset means the Flip-Flop output is set to '1' when the Preset = '0'

Active-low Clear means the Flip-Flop output is reset to '0' when the Clear = '0'

Similarly,

Active-high Preset means the Flip-Flop output is set to '1' when the Preset = '1'

Active-high Clear means the Flip-Flop output is reset to '0' when the Clear = '1'