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Concerning ST-Link on Nucleo Board

Zt Liu
Senior III
Posted on June 08, 2017 at 17:33

hi,  fellows!

I have some questions about ST-Link, especially those on Nucleo boards.

First, I often use the on board st-link link to debug/program some other custom boards, it works fine.

But someday, I'd noticed that the debugger's AIN_1(target VCC) is never  really connected to the MCU VCC

of the application board, for R9 is not lying there. See below:

0690X00000607H3QAI.png

From the UM1075 User manual of ST-Link, it says:

The power supply from the application board is connected to the ST-LINK/V2 debugging and programming board to ensure signal compatibility between both boards.

So is this really unnecessary? (For me, the debugger/programmer works fine so far.)

Or is this risky for some reason?

I really need to know about this!

For we are making a project with the whole nucleo board as a part,

 with st-link on it.

And I've already removed R23 for saving power.

See below:

0690X00000602TEQAY.bmp

Thanks for reading the post!

Zt

#debugger #st-link #programmer #nucleo
5 REPLIES 5
Posted on June 08, 2017 at 20:00

The stand-alone ST-LINK has buffers so that the debugger and the target board can run at different voltages. The NUCLEO/DISCO boards don't have these buffers, and just use/assume the use of 3.0V or 3.3V signalling.

Most of the pins are 5V tolerant, and the VIL/VIH vs VOL/VOH provide a lot of leeway.

The idea would be to avoid back-feeding current into a processor via the GPIO pins and skewing the current measurements.

If the target STM32 were running at 1.25V I'd probably want the buffers

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Posted on June 09, 2017 at 01:14

Thanks Clive, as always!

So since my target MCU is running at 3.0/3.3V, there is a lot of leeway.

Guess I can sleep well with the target VCC pin left open! 

:)

Posted on June 09, 2017 at 11:15

For the STLink on Nucleo and Disco boards, nearly _none_ of the pins used is 5-Volt tolerant! So if you only power the target and not the stlink, the stlink will mostly be back-powered by some pin and target current will increase substantial!

Posted on June 09, 2017 at 11:36

the stlink will mostly be back-powered by some pin and target current will increase substantial!

It's true, and I'd discovered that :

Even the  target MCU is in stop mode, the WHOLE Nucleo board is sinking almost 2mA!

This almost drives me mad, so I disconnect to Vcc Target, Rest pin, and  took off LD3 too. 

Now the whole board, in stop mode, only takes around 20uA with rtc on. 

Posted on June 09, 2017 at 20:54

>>

nearly _none_ of the pins used is 5-Volt tolerant!

I see where you're going with that, the F1 host side is problematic. The target side (SWDIO, SWCLK, SWO) all the parts I looked at are FT pins

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