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IMX6D debug UART weird behaviour

Question asked by Peter Hygren on May 21, 2013
Latest reply on May 28, 2013 by Peter Hygren
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Hi all,

 

Can anyone explain this behaviour:

When trying to boot various uboot images I can read out the debug info just fine. However, if I ever wanna input data to the UART, I get this weird voltage level shift that results in me having to reboot the board. This first image shows the TXD from the CPU (1.8V logic level) in blue. This gets interpreted by my USB-UART just fine as a normal boot log (that crashes, but that's another issue).

20130521_140336.jpg

Now if I try to send data in the other direction (yellow) the data is read correctly by the CPU, but the output signal becomes distorted after the first pulse, and can no longer be read by my USB-UART because of the high LOW-level. See the image below:

20130521_140621.jpg

All sub-sequent responses from the CPU is at this weird high level and I have to cycle power to remove the behaviour.

 

Has anyone got a clue what might cause this?

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