Cannot Connect to STM32F405RGT6 on Breakout (ST-Link V2)

honboxuan · ‎2012-12-25

Posted on December 25, 2012 at 14:43

Hello all,

I created my own breakout board for the STM32F405RGT6, but I'm unable to connect to it via the ST Link V2. The error is ''No Target Connected''.

I've tested this with an external 8Mhz crystal (with load capacitors) and without. All other pins are simple broken out. I've successfully connected to the STM32F4 Discovery using the exact same method.

After some searching, I found that pulling the BOOT0 pin HIGH allows me to see if the device is working. Sending 0x7F at 9600bps 8E1 to USART3 returns inconsistent bytes (changes all the time). On all pins of USART1, there is no response. The same thing on the Discovery board returns the expected 0x79 (on the first try, something else on all others).

This is the first time I've developed a breakout for STM32 devices, and it is possible I've missed a connection required for it to work. So far, it is simply VDD, VSS, PH0, PH1, BOOT0 connected.

Any help will be appreciated! Thank you!

Hon

Tesla DeLorean · ‎2012-12-25

Posted on December 25, 2012 at 20:13

The chip doesn't use the HSE unless your own software enables it.

What about the VCAP pins? Analogue & Digital supplies? Complete schematic?

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honboxuan · ‎2012-12-25

Posted on December 25, 2012 at 21:46

Hello, thanks for replying!

I went and looked through the datasheet again just now and I noticed the VCAP pins need to be connected through 2.2uF, low ESR caps to GND. I've ordered some tantalum caps for these.

I've broken the VSSA and VDDA, so I can tie them to VSS and VDD if necessary (which is, according to the datasheet). I have no clue as to why this is necessary though.

Hon

Tesla DeLorean · ‎2012-12-25

Posted on December 25, 2012 at 23:02

The analogue supply is connected to the power-on-reset circuit as I recall.

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honboxuan · ‎2012-12-25

Posted on December 26, 2012 at 00:12

Thank you! I'll post back when I've fixed everything.

Just curious, the datasheet says the VCAP pins are meant for filtering the main regulator. What main regulator is this? How vital is this filtering to the functionality of the MCU?

Hon

Tesla DeLorean · ‎2012-12-26

Posted on December 26, 2012 at 16:49

The core runs at 1.2V

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ken239955 · ‎2012-12-26

Posted on December 26, 2012 at 17:45

As Clive says, connect VSSA and VDDA.

honboxuan · ‎2012-12-27

Posted on December 28, 2012 at 00:12

Thanks for all the replies.

Unfortunately, it still doesn't work. I previously removed the external crystal which shouldn't affect anything, and here's what I did:

Connected VSSA to VSS, and connected VDDA to VDD. Tried connecting to ST-Link V2, ''No Target Connected''. Tried 0x7F at 9600bps 8E1, USART3 responds inconsistent bytes (and sometimes no response).

Attached 2.2uF, 63V electrolytic caps to between VCAP1 and VSS, same for VCAP2. Tried ST-Link V2, same error. 0x7F to USART3, same type of response.

I probed the voltage at VCAP pins, found them to be ~0.25V at VCAP1 and 0V at VCAP2. This doesn't mean much to me since I don't really know how they are internally connected, so it might be irrelevant information.

For convenience, I'm powering the chip now using the 3.3V output from the FTDI breakout from Sparkfun.

Any suggestions will be appreciated!

Bo Xuan

ken239955 · ‎2012-12-28

Posted on December 28, 2012 at 21:57

Connect VREF+ to VDDA.

oops. Sorry, I see 64-pin LQFP does not have VREF+.

Try 10K pullup on BOOT1 (PB2).

Did you connect all VDD and VSS pins?

On my board I did not connect BOOT0.

Also I read 1.26V at VCAP_1 and 0.24V at VCAP_2.

Edit: Correction, I am reading 1.26V at both VCAP_1 and VCAP_2

honboxuan · ‎2012-12-28

Posted on December 28, 2012 at 22:02

After further searching, these are the connections I've made:

VDDA to VDD

VSSA to VSS

VCAP1 to 2.2uF 63V electrolytic cap to VSS

VCAP2 to 2.2uF 63V electrolytic cap to VSS

VBAT to VDD

NRST to VDD (also tried with VSS, though datasheet suggests LOW for reset)

BOOT0 to VDD

I use the Sparkfun 3.3V FTDI breakout to power the board, and connect RXI to PB10 and TXO to PB11. Using 9600 8E1, I send 0x7F.

I frequently get a 0xFF and 0xFE reply, and also 0xFF by itself frequently. Does anybody know what these mean?

Any assistance will be appreciated!

Bo Xuan