Where to connect SWD VTref?

RE: Where to connect SWD VTref?

Mishka — Mon, 22 Jul 2019 08:04:45 GMT

Right. Thanks guys, you saved me a day (and PCB space :-)

RE: Where to connect SWD VTref?

awneil — Mon, 22 Jul 2019 08:01:58 GMT

That's correct - VTref is an input to the debug probe so that it can sense what voltage the target's debug port is running at.

RE: Where to connect SWD VTref?

Mishka — Mon, 22 Jul 2019 06:54:45 GMT

Okay, I got it. From the target point of view the VTref is output.

It's used by debugger as reference voltage to adjust clock and I/O levels. In this regard, both of the VTref symbols on the schematics above are incorrect. Instead, VTref should be taken from VDD. In case if external power supply required it has to be connected in a usual way. Here they are:

Please correct me if I'm wrong. Thank you!

RE: Where to connect SWD VTref?

Nguyen Hoan Hoang — Mon, 22 Jul 2019 04:34:41 GMT

VDD