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I have made a custom board based on the Arduino Due but have some problems with the Serial communication with the 16u2 chip.

i have usb connection with the 16u2 chip and was able to load the arduino-due usb serial hex over the usb port. the usb now shows up as arduino com port. now when i try to load a sketch it says No device found on COM12. the SAM chip is erased but it can't load the new sketch.

now when i load a sketch with a simple serial print at 115200 over the native port. the SAM chip is programmed correctly. when i open the serial monitor i receive data but it is garbage! the garbage is always different. the sketch is at 115200 and the monitor also at 115200.

this would explain why it can't upload a sketch with the 16u2.

the same sketch on a original arduino due works fine.

the transmit an receive led are blinking.

What would cause this garbage in the connection where do i start looking?

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    You mean the serial speed or the actual chip speed? Commented Apr 5, 2016 at 11:04
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    Alright thank you for the tip! will try to messure the frequency of the TX. Commented Apr 5, 2016 at 11:09
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    Incorrect crystal or incorrect fuse settings. Testing the TX is a good way of measuring the clock speed. You get a ratio of what you want and what you measure, then apply that ratio to the clock speed you want - the result is the actual clock speed. Commented Apr 5, 2016 at 11:14
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    was not able to get a frequency test but did a speed test sketch on a original Due and 2 of my own builds. The Due runs at 6745 Millis and my own at 6281 Millis so it seems to be running slower then the original Due. the crystal used is: link. i don't have any knowledge of fuse settings so will have to read into this. if i have a different crystal would this need different fuse settings than a original Due? Commented Apr 8, 2016 at 20:02
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    I have checked and it seems that they are 12pF and the datasheet for the crystal says it needs a 8pF. Could this be the solution so my problem? Commented Apr 8, 2016 at 20:43

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