Cannot connect to new STM32 on custom board via ST-link

[jackygip]

Posted on August 28, 2015 at 17:59

I've made a PCB which is very similar to that of the STM32DiscoveryF4 schematic but I cannot see the STM32F407 with my ST-Link programmer on either the JTAG or SWD methods.

So far I have soldered only an minimum number of components, namely a few 100nF decoupling caps, STM32F407VGT6Z, crystal/caps/resistors (even though I think it uses the internal oscillator by default?) and programming headers. I have checked that the STM32 has 3.3V and that there are no shorts. As this is my first use of a ST microcontroller, I'm unsure whether I need more components soldered? Can someone confirm? 

The following pins are connected from the PCB to ST-Link programmer:

3v3

GND

JTMS-SWDIO

JTDI

JTCK-SWCLK

JNTRST

JTDO

NRST

I've tested my ST-Link programmer and the pinouts by using it on my STM32F4Discovery whist the built in ST-Link disabled and it worked fine.

Any other ideas?

Is there a way to check if the internal oscillator is working through external pins?

Am I forgetting something? BOOT0/BOOT1 resistors needed?

Cheers

#stm32-st-link

[Tesla DeLorean]

Posted on August 28, 2015 at 18:10

You know, this type of topic has been covered over and over here, have you looked at some of those?

Make sure the analogue supplies are connected.

Make sure you have caps on the VCAP pins, AND that you can see 1.25V there.

What voltage do you see on the NRESET pin?

Pull-up on NRESET, Pull-down on BOOT0 and BOOT1 (I'm not going to argue necessary vs desirable)

[jackygip]

Posted on August 29, 2015 at 09:59

Thanks Clive, I followed your steps with a fresh PCB and STM32F407VGT6Z, and now it's working, ST-Link can pick it up on both JTAG and SWD modes.

For reference, my list of the minimum number of components required for ST-Link to work on fresh STM32: 

2.2uF on VCAP1/VCAP2 (1.25V at both)

Connected VDDA and VREF+ to VDD 

VSSA and VREF- to GND

A few (3) 100nF decoupling caps

No crystal

Programming headers

1k pull downs on BOOT0/BOOT1

LED and resistor connected to STM32 VDD supply

ST-Link Connections to PCB (This can be reduced to just power and either JTAG or SWD pins):

3v3 (ST-Link supplying power to PCB, ST-Link pins 1, 2 and 19)

GND (4, 6, 8, 10, 12, 14, 16, 18, 20)

JTMS-SWDIO (7)

JTDI (5)

JTCK-SWCLK (9)

JNTRST (3)

JTDO (13)

NRST (15)

I was curious about the VCAP capacitors so I removed them from my discovery board with nothing but USB connected and it still operated as expected. Obviously removing the VCAP's is not desired.

I should also that before I begun the 2nd PCB, I checked of the 1st PCB and NRST it seems to be 3.3V when ST-Link just connected to USB, but once you try to connect to stm32, it is pulled low when there is a connection error and doesn't release until ST-Link power cycled.

[LMI2]

Posted on August 29, 2015 at 13:13

This is useful information.

About 100nF caps. A friend of mine has, I think,  F100 or L100 board working reliably without those capacitors. That is heretic of course, he says that if it works without them, they should be left out. True Belivers like I know that every plus pin must have a 100nF connected to ground. One less and the board stops working. (I once made an Atmel board where one supply pin was floating, (because I forgot it). The board worked normally.)

Regards

Leif M