SN74LVC1G99: Logic function of XNOR not available

Hi Peter,
Your schematic is correct -- that means the issue would have to be somewhere else in the system that you aren't showing me. It could be something as simple as a short, or it could be a more complex issue like ESD damage to the output of the SN74LVC1G99, or a load that can't be driven by this device.

I would recommend starting by checking that the inputs are doing what you expect on an oscilloscope, and monitor the output and supply to see if either fluctuates during operation.

Next I would start looking closely at everything connected to the traces or wire that has the erroneous signal on it.

If you can provide a complete schematic and layout, i can try to see any issues from here.

I'm sorry that I didn't reply to you in time because of my business trip two days ago.
Because I can't upload pictures, I directly dictate the connection mode of the test circuit. The IC PINs 1,2,3,4,5,are directly connected to ground. PIN 6 pull-down and connected to a switch and then to the power supply(5V). PIN 7 as output point. PIN 8 connected to the power supply(5V).
I used an oscilloscope to measure the input voltage at all test points correctly, except the output point.
When I change the logic of PIN6(D),there is no logical change at the output point (Y). This result is different from the truth table I queried in the data manual.
I wonder why. I've tried many usual testing methods. All the output points have no logical output. I also changed several chips.
If there is no problem with the chip you are testing, can you send the test circuit to me for reference?
Thank you very much.

Hi Peter,

You can upload images on e2e. It would be very beneficial to us to see some scope shots of your operation.