Raspberry Pi Debug Probe documentation needs clarification

[seamusdemora]

I'm trying to connect my new Debug Probe to an (apparently) older Pico. IOW, my Pico does not have the 'JST' connector at the SWD terminals; it has only 3 holes, and I've soldered a 3-pin header in that location for making connections.

I am trying to follow the online documentation for making the required connections. However, the documentation assumes the existence of the JST connector at SWD, and does not indicate how the female headers are to be connected to the SWD. The middle GND connection seems clear enough, but which wire goes to SWCLK and which one goes to SWDIO is unclear. I've been unable to find any markings that make these connections clear.

Can someone clear this up for me?

[P33M]

SWCLK/SWDIO are marked on silkscreen on the underside of the board.

[lurch]

ping @aallan in case the documentation needs clarifying.

@seamusdemora See also Chapter 5 of https://datasheets.raspberrypi.com/pico/getting-started-with-pico.pdf (which unfortunately doesn't cover the Debug Probe yet). There's also pinout diagrams at https://www.raspberrypi.com/documentation/microcontrollers/raspberry-pi-pico.html

[seamusdemora]

@P33M , @lurch

Thanks, but the problem is actually in the documentation. Nowhere is it pointed out which pin from the debug probe goes to SWDIO, and which goes to SWCLK. I finally surmised from the box that the C in TX/SC was for SWCLK, but that seems a bit of a reach. And I guess there are still a lot of non-JST Picos out there!

[lurch]

Yeah, perhaps this NOTE block needs a bit more clarification?

But do note that https://github.com/raspberrypi/documentation/pull/3454 changes the "SWDCLK" wording to "SWCLK", so hopefully that makes it a bit more obvious that SC from the Debug Probe connects to SWCLK on the Pico, and SD from the Debug Probe connects to SWDIO on the Pico? :shrug: See also https://www.raspberrypi.com/documentation/microcontrollers/debug-probe.html#the-debug-probe

[seamusdemora]

Yes, the NOTE block would be a good place to put some clarification in the "Getting Started Guide", and IMHO it needs a picture to support the point. It should unequivocally establish the point that the Wire labeled SC is to be connected to the board terminal SWCLK, and the wire labeled SD is to be connected to the board terminal SWDIO.

With 100's of thousands of graphics like the one below still floating around on the Internet, it seems to me the users/customers deserve clarity. It will be years before the non-JST-equipped boards disappear.

Just my 2 pence worth...

[lurch]

It will be years before the non-JST-equipped boards disappear.

Correct. The "non-JST boards" are Pico and Pico W, and the boards with the JST debug headers are Pico H and Pico WH. All 4 boards serve different purposes, and as it says at https://www.raspberrypi.com/products/raspberry-pi-pico/ "Raspberry Pi Pico series will remain in production until at least January 2034".

[seamusdemora]

@lurch Ah! Did not know that... I thought the "older/original" Picos had been phased out in favor of the new. All the more reason to fix the docs, eh? :)

[lurch]

https://shop.pimoroni.com/collections/pico-w-aboard is an example of where the Picos-without-headers are useful. See Chapter 3 of https://datasheets.raspberrypi.com/rp2040/hardware-design-with-rp2040.pdf for more information.