SN74HC165: Logic Gate used in the SN74HC165 + behaviour at missing connection to the supply voltage or ground

user6278963

Part Number: SN74HC165
Other Parts Discussed in Thread: SN74LVC1G74

Hi,

I wanted to know what kind of logic gates are used in the shift Register SN74HC165. In the datasheet it looks like a RS Flipflop, but has an additional input for digital data. What is the exact name of this logic gate?

I also did some tests on the shift register and noticed, that if I seperate the connection to the supply voltage my Register still works without any malfunction. This also happens when I seperate the Connection to ground and the supply voltage is connected.

Can you help me out with this?

I also post my circuit here.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 212120 points

Those are D-type flip-flops with asynchronous preset/clear inputs; they behave like the SN74LVC1G74.

When you disconnect V_CC and/or GND, supply current can still flow through the ESD protection diodes; see EEVblog #831 - Power A Micro With No Power Pin!

0 user6278963 over 3 years ago in reply to Clemens Ladisch

Prodigy 40 points

Thanks for your answer so far.

So there is a mistake on the datasheet by the naming of the logic gates?

0 Clemens Ladisch over 3 years ago in reply to user6278963

Guru 212120 points

Where does the datasheet name logic gates?

0 user6278963 over 3 years ago in reply to Clemens Ladisch

Prodigy 40 points

You're right, in the funtional block diagram chapter 8.2 there is no exact Designation of the logic gates, but the R & S reminded me of a RS flip flop...

Maybe the R & S should be some abbreviations for preset and clear. Is this possible?

0 Clemens Ladisch over 3 years ago in reply to user6278963

Guru 212120 points

They are abbreviations for "Reset" and "Set". And they work exactly like in an SR latch …

0 user6278963 over 3 years ago in reply to Clemens Ladisch

Prodigy 40 points

But why did you said that the logic gates are D type flip-flops with asynchronous preset/clear Inputs?

Because there is no set and reset on a D type flip flop.

0 Clemens Ladisch over 3 years ago in reply to user6278963

Guru 212120 points

How else should I describe a flip-flop with a clocked D input? (The R/S inputs are not clocked.)
And that is how TI describes the SN74LVC1G74.

0 Dylan Hubbard over 3 years ago in reply to Clemens Ladisch

TI__Mastermind 41010 points

Hi,

I see a few answers marked as resolved in this thread, this typically indicates that the was sufficient to fix the issue at hand. Are you confused with the device operation itself? If not, it seems like this thread can be closed and locked.

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SN74HC165: Logic Gate used in the SN74HC165 + behaviour at missing connection to the supply voltage or ground