ST-Linkv2 on STM32F3 Discovery

[axel2]

Posted on June 08, 2015 at 16:33

Hello,

I've been using STM32 for quite some time. In work I use full ST-Link v2 isol but, in home as hobbys (and soon startuper) I use stlink on stm32f4 disovery board. I had no problems with it untill today. 

When my external board is fully powered by Disco. (is connected to 3V and GND) everything works. I can flash it, erase etc. 

However when I connect external power supply to external board (which is 3V45) I cannot connect to device. With STM32 utility I get ''Can not connect to target'' but still I get Device ID, and type but cannot flash it or read memory. 

Questions are:

1) Is it normal?

2) If I get full ST Link v2 (not isol) will it help?

#stm32f4 #discovery #stlink

[Tesla DeLorean]

Posted on June 08, 2015 at 18:23

Just connect the GNDs together to provide a return path for the electrons.

Don't connect two different supplies together.

The stand-alone ST-LINK requires target power because it uses this for a signal buffer chip, this doesn't exist on the DISCO, where the 3V used by the driver will be just find, and the signal back from the target will be just fine.

[axel2]

Posted on June 09, 2015 at 08:29

Hello Clive,

Grounds are connected, just like Target_Vdd signal. In fact all SWD signals are connected (even additional SWO). 

I'm not mixing supplies, I use either of them, either external or discovery one.

''where the 3V used by the driver will be just fine'' - well it's not really fine, I DO require at least 3V3, but everything above is nice and assures proper interoperation with analog part of circuit.

I supposed that standalone STLink has voltage buffer, and now I'm sure. The only question is, what is the purpose of putting Target_Vdd signal if embedded (on disco.) programmer cannot handle anything except for pure 3V.

[Tesla DeLorean]

Posted on June 09, 2015 at 17:18

3V CMOS signalling on SWO, SWDIO, SWCLK into a 3V3 part will work just fine in terms of levels, and recognizing high and low states.

Powering is another issue, and if the target device is non-functional, the SWD/JTAG connectivity will fail. With the DISCO you're going to have to make sure you've broken whatever links and solder-bridges connect it to the local target before you connect it to an external one.