I have a very simple app that generates a sine wave, the scope trace is fine.

I decided to replicate the logic so I could generate two signals by leveraging the second DAC.

Problem is that the output from the 2nd DAC is clipped whereas the first is not.

This is running on a Nucleo F446RE board.

DHR12R1 appears a perfect looking sine but DHR12R2 has clipped (just the top) at slighly less than 3v.

Can anyone see anything in the code that might explain this?

(The writes to the 2nd DAC are "inverted" so that the two signals are 180 degrees out of phase just FYI).

Here's the code (the collapsed stuff is the sine table calculation, no IO at all).



Writing to just DAC1 or DAC2 and the clipping is still present but only when writing to DAC2.

 

I would have thought 4095-X rather than 4096-X.

I doubt that this is the cause of your main problem though.

 

I would have thought 4095-X rather than 4096-X.

I doubt that this is the cause of your main problem though.

Yes, you're right!

But as you suspected that isn't the cause (making them both simply [X] shows the problem still)

 

As you probably already guessed - I have no idea what I am talking about, but that won't stop me

No idea why you have delay(); call after first DAC setting, but seems morally wrong to have no second delay(); call after second DAC setting.

Somebody knowledgeable will be along soon....

 

(The writes to the 2nd DAC are "inverted" so that the two signals are 180 degrees out of phase just FYI).

If the SINEWAVE function takes values of 0-4095, then 4096 - X is out of range for X=0. Maybe subtract from 4095 instead of 4096?

Edit: I should refresh before posting...

 

As you probably already guessed - I have no idea what I am talking about, but that won't stop me

No idea why you have delay(); call after first DAC setting, but seems morally wrong to have no second delay(); call after second DAC setting.

Somebody knowledgeable will be along soon....

Simply to get the signals slightly out of phase, so I can visually compare them easily.

 

OK the schematic for the board shows that PA5 is already connected to the Green LED...

I guess its acting like a kind of zener diode from what I can find on the web.

 

The DAC outputs can only drive 5kΩ or higher. Any excessive loading will cause the output to be clipped.

Edit: Remove SB21.