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ST-Link/V2 - power output *to* target?

Andrew Neil
Evangelist III
Posted on September 21, 2015 at 10:45

Is the ST-Link/V2 able to supply power

to

the target?

The UM1075 User Manual is not at all clear on this.

AIUI, 'VAPP' (pins 1 & 2 on the 20-pin JTAG/SWD connector) provides the supply voltage

from

the target; ie, it is an input to the ST-Link.

This is in accordance with the standard ARM 20-pin JTAG pinout.

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0499b/BEHEIHCE.html

But 'VDD' (pin 19 on the 20-pin JTAG/SWD connector) is not at all clear - is this an input or an output?

Whatever it is, this is

not

in accordance with the standard ARM 20-pin JTAG pinout.

On the Keil (an ARM company) uLink, this pin is Not Connected:

http://www.keil.com/support/man/docs/ulink2/ulink2_hw_connectors.htm

#st-link-power #pinout #ulink #jtag #st-link #stlink #stlink
9 REPLIES 9
Posted on September 21, 2015 at 14:51

Segger's J-Link has been using 5V on pin 19 for a very long time. It's been a way of USB/JTAG powering a lot of boards.

While ARM has defined the functions of pins 1 & 2, there's been all manner of interpretations in different boards over the years. Pin 1 should be the board's own supply, and this is often used in buffering circuitry on the pod.

I'm not sure it's valid to bond 1 and 2 unless the pod is powering the board, at that voltage.

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/user_manual/DM00026748.pdf

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ingwmeier
Senior
Posted on September 21, 2015 at 14:59

Hi Andrew,

I modified some Nucleo Boards in order to have a powered programming adapter. The target there needs to be powered through the Voltage Regulator of the User Part, otherwise USB connection is lost when attaching your target device. The STLINK V2 adapter does not supply your target unless you do it yourself using a seperate 3.3V source (good old manual patch work). The internal source normally also suffers from the USB lost problem. Using an old Keil ULINK ME Board in a different setup was ok with an additional 1000uF Cap across 3.3V local power supply.

Regards

Werner

0690X00000602a1QAA.jpg

Andrew Neil
Evangelist III
Posted on September 22, 2015 at 10:40

@Clive: Yes, that link is the ''UM1075 User Manual'' to which I referred - it says nothing helpful.

It just says that it's ''3.3V'' on pin 19 - no indication of whether it's in or out; or, if it's an out, whether it's suitable to power the target.

Andrew Neil
Evangelist III
Posted on September 22, 2015 at 10:51

@Werner:  I should clarify that I'm talking about the standalone product - as described in the mentioned User Manual - not the integrated things found in Nucleo & Discovery boards.

Posted on September 22, 2015 at 13:28

I think it establishes that Pin's 1 & 2 of the pod are INPUTs (bonded together, the supply FROM the Target Board) and Pin 19 is an OUTPUT. Now perhaps it's doesn't have the clarity we'd all like, and it doesn't give a current specification, but I think it can be inferred and confirmed.

At least some of the boot-leg ones use an LM1117IMP-3.3, which is rated at 800mA.

Like I said sticking power out of Pin 19 is not a new phenomenon, Segger's been doing it for very many year, and IAR/Olimex have been using that to power boards from the pod for as long. I've got one of these STR912 from 2007 that does exactly this. 

https://www.segger.com/iar-str912-sk-eval-board.html

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Andrew Neil
Evangelist III
Posted on September 22, 2015 at 15:25

''I think it establishes that Pins 1 & 2 of the pod are INPUTs (bonded together, the supply FROM the Target Board)''

Yes - agreed.

''and Pin 19 is an OUTPUT''

No; I don't see how that can be inferred from the manual.

''perhaps it doesn't have the clarity we'd all like''

Ha ha - to put it politely!!

''and it doesn't give a current specification''

Indeed

''but I think it can be inferred and confirmed''

Not from the manual.

''At least some of the boot-leg ones use an LM1117IMP-3.3, which is rated at 800mA''

Yes - as it happens, that is at the root of my question!

''Like I said sticking power out of Pin 19 is not a new phenomenon, Segger's been doing it for very many year''

I'm not so familiar with Segger - so wasn't aware of that.

But, thanks - it helps.

I'm sure I've seen a comment along the lines of , ''unlike Segger, ST-Link only gives 3.3V'' - which certainly supports the case.

''IAR/Olimex have been using that to power boards from the pod for as long''

Cheers - I think you have persuaded me by now.

🙂

From: neil.andrew

Posted: Tuesday, September 22, 2015 10:51 AM

Subject: ST-Link/V2 - power output *to* target?

@Werner:  I should clarify that I'm talking about the standalone product - as described in the mentioned User Manual - not the integrated things found in Nucleo & Discovery boards.

Posted on September 22, 2015 at 16:24

I think you have to be careful with ''The Standard Says This'', the reality on the ground is often very different. I suspect ARM thought that power from the pod to the board would come from Pin 2, but this all devolved very quickly with a lot of half-assed board implementations where people got this all very screwed up. The last thing you want is the debug pod to cause a massive short on the board, or burn things up.

Over the years I've learned to read between the lines, perhaps it's my dyslexia, but sometimes it comes from not saying something, the way it's phrased or ordered, and what's the simplest or most likely out-come. I try to picture the engineer talking to, and explaining the functionality, to a technical writer.
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Andrew Neil
Evangelist III
Posted on September 22, 2015 at 16:29

Yes - that's why the 

ST

  User Manual should clearly document what the 

ST

  product does.

It's the lack of information in the 

ST

  User Manual that I'm complaining about.

Andrew Neil
Evangelist III
Posted on October 01, 2015 at 14:01

I can confirm that Pin 19 of my STLink will, indeed, power my target.

🙂