Vdd on Particle debugger debug ribbon cable - Is it Vref OR 3v3 supply


#1

Hi, I am converting from Blackmagic Probe to the new Particle Debugger NanoV2

My questions are
i) is there a schematic for the Particle Debuggerr

ii) I am not using the headers on the Particle Debugger. Is the JTag ribbon cable Vdd pin a Vref sense for the device under test? The mbed docs show Vref on this pin
I can measure 3.3V on that pin and am concerned that if I power my device under test from its own supply there will be a conflict in supply volts.


#2

Does this help?
https://docs.particle.io/datasheets/wi-fi/argon-datasheet/#swd


This is the pinout of the receptacle on the mesh devices.
Since the 3.3V rail on the devices is not tolearant to higher voltages 3.6V you should be safe.

I did search for the schematic of the debugger, but couldn’t find it either - maybe @rickkas7 knows where to find it.
Also looking at this promo pic, it’s safe to have the LiPo attached while debugging
image
And from that I’d deduce that it’s safe to power the device from an alternative source.
I’ve done it via USB and didn’t have my device go up in smoke :wink:


#3

Thanks for that.
I am looking at using the Particle Debugger to replace the much more expensive BlackMagic Probe in this Easy Very Low Power BLE in Arduino project

Part of that project is to use ‘bare’ nRF52 chips (antenna but no regulator) with alternative power supplies.
The BlackMagic Probe does not supply power but does monitor the nRF52 power to set the probe’s I/O levels

Looking at this page https://docs.particle.io/support/particle-tools-faq/jtag/ I see
header

Which suggests Vdd supplies 3V3 rather then monitoring the nRF52 volts, but a circuit diagram of the debugger would be nice.


#4

I agree. I was surprised not to find one in the github repo.


#5

VDD is a 3.3V supply pin, not a sense pin like the ST-LINK/V2.

It can certainly power a mesh device only from the debugger, but it probably should not be used with an external power supply at the same time. The picture with the LiPo attached is probably not a good configuration.

I’ve used it with both the debugger and the USB serial attached and powered and it did not burst into flames, but it’s probably not a good idea to do that either.

I would have preferred the switch to be able to turn off VDDF (fused VDD, the 3.3V supply via the debugging connector) but that’s not what it does.


#6

Thanks for the info.

What I will do is ALWAYS power the Nano externally with 3.3V supply when programming and not connect the Debugger Vdd lead, and add 2K7 resistors in series with SWCLK, SWDIO, TX and RX lines. And of course connect a GND lead.

The 2K7 resistors are to protect the nRF52 chip from the Debugger outputs when the Debugger is powered and running and the Nano has not been powered up, and visa versa.

Edit: 2K7 too high to allow programming via SWCLK, SWDIO,
1K works