SN74LV273A: Initial state

Shuji Ishiwata

Part Number: SN74LV273A
Other Parts Discussed in Thread: SN74LVTH273, SN74HCS273,

Hi All,

I have a question about SN74LV273.
I think the initial state is undefined, but is it okay to pull down the output to avoid that?

Best Regards,
Ishiwata

10 months ago

0 Malcolm Lyn 10 months ago

TI__Mastermind 21230 points

A pull-down will not work. The only guaranteed way to preset the logic level with this device is to use the clear pin or clock in data.

You can also try using a bus-hold device with a pull-down resistor on the output, such as the SN74LVTH273 or SN74LVCH273. Please see section 6.3 in the document below:

https://www.ti.com/lit/an/scla015b/scla015b.pdf

+1 Shuji Ishiwata 10 months ago in reply to Malcolm Lyn

Mastermind 6985 points

Thank you for your answer.
I understand that the initial value is not undefined for devices with a bus hold function.
Since SN74LVTH273 is an old product, I would like to suggest SN74HCS273, but is it a good idea?

0 Malcolm Lyn 10 months ago in reply to Shuji Ishiwata

TI__Mastermind 21230 points

The HCS does not have bus hold, so you will not be able to define a state on powerup with this device. If that doesn't matter and all you are looking for is a more recent device, then there is nothing wrong with the HCS273 (without knowing anything else about the system requirements).

0 Shuji Ishiwata 9 months ago in reply to Malcolm Lyn

Mastermind 6985 points

I have an additional question.
I understand that if you input an assert signal to the CLR pin of SN74LV273A using a reset IC, etc., and release the clear after the power is turned on, the output will be low until CLK is input. Is this understanding correct?

+1 Clemens Ladisch 9 months ago in reply to Shuji Ishiwata

Guru 294220 points

Yes. (This is the main purpose of the /CLR input.)

0 Shuji Ishiwata 9 months ago in reply to Clemens Ladisch

Mastermind 6985 points

Thank you for confirming.
And, Thank you for your answer.

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SN74LV273A: Initial state