Does the input have already a Schmitt-Trigger?

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Figure 10-5 in the ATMEGA32U4 datasheet seems to say all the digital inputs have schmitt trigger.

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Why do you ask? The reason I ask is because what you are asking may not be important to what you need to do.

Can you explain what you are trying to do?
 
Why do you ask? The reason I ask is because what you are asking may not be important to what you need to do.

Can you explain what you are trying to do?

I feed a teensy 2.0 with a external clock of an old device. Some of the devices have a dirty clock signal, so I have to set the low pass filter of the clock lower. This helps on most devices, but on some not.
I notice that, if I change the filter only, get an DC offset of 0.5V and maybe this is too short on the threshold and in some cases it does not work.
I have no idea where the input switch to high and back to low.
 
If you are looking for an exact value, I think it is somewhat arbitrary by nature.

The problem is that the Schmitt-Trigger is defined internally to the chip, not some dedicated manufactured part.

If you need to know, and it's not in the chip's data sheet, then I would put in a request with technical support at NXP. Even then, they may not have a definitive answer, but that is the best you can do.

Otherwise, you can look up a number of different Schmitt-Trigger chips and take the average, but that is only an educated guess.
 
Of course, but a sample size of one isn't very telling, statistically speaking.

There may be other factors that could cause that empirical value to change under different conditions, too. That might be a bigger problem if the operation becomes intermittent.

I am guessing it may be better to condition the signal externally than to rely on unpublished functionality. That, and to the best of my knowledge a Schmitt-Trigger only deals with level hysteresis, and that may not help with ringing of a signal.
 
Of course, but a sample size of one isn't very telling, statistically speaking.

There may be other factors that could cause that empirical value to change under different conditions, too. That might be a bigger problem if the operation becomes intermittent.

I am guessing it may be better to condition the signal externally than to rely on unpublished functionality. That, and to the best of my knowledge a Schmitt-Trigger only deals with level hysteresis, and that may not help with ringing of a signal.

Sure, but then the OP was talking about a single T2.0 and asking if it was Schmidt Triggered.
 
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