I just finished assembling my PCB with an ATSAMD21G18A and was super thrilled to flash it with my program. Sadly Atmel Studio tells me that it can't find the device.

I tried to debug the whole thing, but I still don't have it working. I think I'm missing something.

What I have:

  • I can read the target voltage in Atmel studio, and it seems to be good (3.3v)
  • I can measure VDD_Core at ~1.2V, which is nominal.
  • I can measure the SWDIO and SWCLK signals on the JTAG (presumably sent from the Atmel ICE)
  • I double checked that the JTAG is connected to the SAM connector and not the AVR connector (did that mistake before)
  • The power supply is showing about 2mA current draw. (not a lot, isn't it)

What i'm missing:

  • Somehow the external clock doesn't start to swing. I don't know what the default setting is, if it should start to swing with a unflashed uC or not. I can't read the Device ID or read from flash in Atmel
  • Studio (Error: Device not found).

The clock not swinging is my biggest worry, but the ATSAM should have an internal clock to work on, right?

The program I'm trying to flash is a example code for the SAMD21 eval board (LED_TOGGLE).

Do you have any idea why the uC might not be working? I have to admit, that this is the first time I've tested this PCB, so it might as well be another issue.



  • 1
    \$\begingroup\$ Please upload a higher resolution image of your schematic. I can't read it. \$\endgroup\$ Nov 11, 2022 at 18:47
  • \$\begingroup\$ Looks like you've checked most of the obvious things. Did you get the ATSAMD21G18A chip from a reputable source? \$\endgroup\$ Nov 11, 2022 at 19:24
  • \$\begingroup\$ Suggest comparing it to the closest dev board schematic that can be found. Also see if the chip has any stepping/revision/silicon eratta documents. \$\endgroup\$
    – rdtsc
    Nov 11, 2022 at 20:08
  • \$\begingroup\$ The Schematic should be more or less the same as on the Arduino MKR1310. The Chip is from Digikey, so I’m not worried about authenticity. \$\endgroup\$
    – Felix Kunz
    Nov 11, 2022 at 20:53
  • \$\begingroup\$ Double check your part number and footprint/schematic symbol - very easy to get this messed up. Placement and selection of the bypass capacitors is fairly critical. I got involved in diagnosing a poor pcb layout that used a sam21l and it came down to this. \$\endgroup\$
    – Kartman
    Nov 12, 2022 at 4:34

1 Answer 1


So, after a lot of searching, i found the problem.

And of course it's a stupid fault in my schematic. You can barely see it on the screenshot, but the SDA and SCL lines for the JTAG were switched.


  • Don't switch these lines

  • Post better screenshots

Thanks for all your help. I'll keep the question up, in case anyone has the same issue sometimes.


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