SN74LVC1G374: what is the state of Q when QE change from H to L?

Harry Ma

Part Number: SN74LVC1G374

Hi Team

At the beginning, QE input H and CLK is High too. Does Q output Z?

Then what does Q output when QE change from H to L and CLK remains H output? Customer thought Q's output will remain at Z, but it outputs L level sometimes. is it normal?

schematic and waveform are shown as below.

Thanks!

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 317390 points

After power up, the initial internal state is either H or L, randomly. See [FAQ] What is the default output of a latched device? (Flip-Flop, latch, register)

When the /OE input goes low, Q outputs the internal state, either H or L.

The only way to get a known output state is by setting it with D and CLK.

0 Harry Ma over 3 years ago in reply to Clemens Ladisch

TI__Intellectual 2660 points

Hi Ladisch

Thanks for your sharing

So Q output Q marked in red means Q output internal state?

+1 Clemens Ladisch over 3 years ago in reply to Harry Ma

Guru 317390 points

That table entry says that the output does not change. This is misleading, because pulling /OE low does make it change.

Anyway, the latch always has a state, either high or low. With /OE, you can prevent that state from being shown at the output pin, but the state is still there, internally.

0 Harry Ma over 3 years ago in reply to Clemens Ladisch

TI__Intellectual 2660 points

Thanks Ladisch

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SN74LVC1G374: what is the state of Q when QE change from H to L?