Use nucleo-64 ST-Link debugger for another MCU

[vernture]

Removed the ST-Link plastic jumpers and all four pins are free now - as shown on the blue rectangle. As well as, the yellow rectangle shows the 6 pins of CN4 on one column.

It seems that pins 1 and 3 are 3.3 V and GND respectively based on the use manual (https://www.st.com/resource/en/user_manual/um1724-stm32-nucleo64-boards-mb1136-stmicroelectronics.pdf) 

but when I check those two pins using a multimeter I get no voltage! Any idea where is the issue?

[mfgkw]

VDD is not driven by the ST-Link, but has to be connected to power of the MCU to be flashed/debugged.

This might be 3.3V or another voltage, depending on your board.

ST-Link reads this voltage.

Only if the jumpers are NOT removed then the ST-Link is connected to your MCU on the NUCLEO and VDD is delivered from there (one of the removed jumpers routes VDD).

[vernture]

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@mfgkw wrote:

Only if the jumpers are NOT removed then the ST-Link is connected to your MCU on the NUCLEO and VDD is delivered from there (one of the removed jumpers routes VDD).

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That's odd to me because the USB power is connected to CN1 of ST-Link part and pins 1 and 3 (from the top) give zero voltage even if I put those jumpers back.

My purpose is to make the connections below to use the Nucleo's ST-Link debugger for a code that's going to program the Blue Pill.  

Nucleo ST-Link   |   Blue Pill
--------------------------------------------
VDD_TARGET  =>   3.3V
SWCLK             =>   PA14
GND                 =>    GND      
SWDIO             =>    PA13
NRST               =>     NRST

When I connect these, the blue pill's power LED doesn't turn on so it doesn't receive power from the ST-Link. 

My board, as shown from the image in the first post, is Nucleo-64 STM32F411RE. 

[Andrew Neil]

As @mfgkw said, and as shown in the table you quoted, pin 1 is VDD from the target - it does not supply power to the target:

To be really sure that the ST-Link is fully disconnected from the STM32F411RE on the Nucleo board, you can break-off the ST-Link part:

Picture credit: @MM..1 via https://community.st.com/t5/stm32-mcus-products/3-3v-power-supply-for-nucleof103/m-p/657826/highlight/true#M240024

PS:

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@vernture wrote:

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That's odd to me because the USB power is connected to CN1 of ST-Link part . 

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Not directly:

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@vernture wrote:

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the blue pill's power LED doesn't turn on so it doesn't receive power from the ST-Link. 

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That is the expected behaviour.

[vernture]

Thank you, but I'm still rather confused what to do.
I don't want to break off the ST-Link part (because I have projects working with the Nucelo board); I just need to disconnect (perhaps using the jumpers) the ST-Link from the Nucelo part and use the St-Link part for the Blue Pill as said earlier. So for that:

1- What jumpers should I remove? Are the two ones of CN2 enough?

2- What pins of the ST-Link should I connect to the Blue Pill's pins? Are they still those 6 pins of CN4!?  

[mfgkw]

There is no need to break the board off.

- Remove the two jumpers

- connect at least VDD_TARGET, GND, SWCLK, SWDIO and NRST between your blue pill board with CN4 of the ST-Link

- if you need Traces via ST-Link then connect SWO as well

- power your blue pill board from any source

- power and connect the ST-Link via USB cable to the PC

[Andrew Neil]

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@vernture wrote:

I don't want to break off the ST-Link part (because I have projects working with the Nucelo board);?  

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You can still use it with the rest of the Nucleo board - you just have to connect via wires as with any other target.

The important thing to understand is that these 6 pins do not provide power to the external target - you will have to power the external target (your Blue Pill) separately.

I think you'll find that breaking off the ST-Link is the best option - because there are still some other connections left to the rest of the Nucleo board.