[ABANDONED] J-Link EDU reads wrong VTref and cannot connect to target

bily · Oct 19th 2016, 6:31pm

Hi,

I am trying to connect my J-Link to a RedBearLab BLE Nano via SWD.
I connected VTref, GND, SWDIO and SWCLK to the corresponding pins on the board, but, even though the board was powered and had 3.3V on VDD (which was connected to VTref), J-Link commander showed VTref = 0.000 V.
I then tried powering the board via J-Link (pin 19 linked to Vin), and in this way VTref was around 5 V, which should be impossible since the board can only have 3.3 V on Vdd.
In both cases I got "Can not connect to target" when trying to connect to the board.
Can you please help me figure out why it doesn't work?
Thank you.

[img]https://static1.squarespace.com/static/5039e08be4b00cf0e8cf88cd/t/541d40b1e4b06fd9d8333e0f/1411203249422/?format=500w[/img]

SEGGER - Alex · Oct 19th 2016, 10:29pm

Hi,

I am 99.9% confident that there is *no* problem on the J-Link side.
Did you make sure that GND is connected properly to the J-Link EDU?

Pretty sure it is a wiring problem. The VTref measurement of J-Link EDU is working fine.

Best regards
Alex

bily · Oct 20th 2016, 9:12am

Thank you for your answer. I connected GND (4) of the J-Link to the GND pin of the board, is that the proper way to do it?

SEGGER - Alex · Oct 21st 2016, 9:58am

Yes, that's O.K.
Can you please try the following?:
Disconnect your target and everything else from the J-Link EDU.
Connect GND and 3V from an external power supply to pins 1 & 4 of J-Link EDU.
Start J-Link Commander
Does it show 3V?

Try the same with 5V or 3.3V etc.
Does J-Link Commander show the correct voltage?

If yes, it shows that the VTref measurement is O.K. and the problem is on the board circuit / wiring.

Best regards
Alex

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