STM32L082(CMWX1ZZABZ-078) not conneting to ST Link

[CChul.1934]

Hi, I have designed a custom board with some sensors and a CMWX1ZZABZ-078 chipset as MCU and Lora module. To design the board I have copied the schematic that Murata has in the datasheet of the module, I'm trying to connect the board to the computer to flash my code but ST link is always giving me the same error (Can't connect the target), I tried with a 10k pull up resistor connected to the MCU_RST pin but didn't work. I cant find the reason why this is not working, any ideas?

Thanks in advance for the help.

[Tesla DeLorean]

Schematic hard to decipher, RF on PCB doesn't look good either.

Create a PDF from the KiCad you're using, as mine doesn't show the Murata module or any pin designations.

[CChul.1934]

Hi, thanks for replying. This is the schematic in pdf. About the RF, I understood that I need a 50 ohms impedance at 868 MHz for impedance matching so I calculated the values of the capacitor and coil to get the 50 ohms at 868 MHz, isn't this right?

Thanks for your help.

[Tesla DeLorean]

Ok, that looks reasonable enough. Are you connecting to a stand-alone ST-LINK, or one on a NUCLEO/DISCO? If the latter make sure to pull the jumpers to disconnect the local target MCU

Check the voltage observed on NRST, make sure JP9 powers VREF

RF is wave energy, you really want broader traces, constant width, curves not sharp corners, and be relatively short. Think of how water moves in a wave tank, you don't want odd reflections, and interference patterns. Impedance matching controls how it flows from one pipe to the next, and consistency end-to-end.

[CChul.1934]

I'm using a stand-alone ST link, this one: https://www.adafruit.com/product/2548. JP9 is power to VREF (3.3V) and MCU_NRST voltage is around 5 mV (Is this the expected value? Should it be higher?). I saw that in some websites people connected a 10k pull up resistor to MCU_NRST pin to get 3.3V when the button is release and 0 when it's pressed but using this configuration didn't work either (I tried it with the ST link RST pin connected to the board and also without it).

Thanks for the piece of advice about RF design.

[CChul.1934]

.

[Uwe Bonnes]

If the Target CPU is in (deep) sleep, you need to connect under reset!

[CChul.1934]

I know, I connect the device Under reset-Hardware reset but it says that can't connect to the target. At this point I'm quite clueless because I can't identified where is the mistake that I'm making.

[Flavio Alves]

Did you find an answer for your problem?

I recently designed a board using the same module and I am facing the exact same issue.

I checked the VREF is powered by VDD (3.3V)

I checked the NRST voltage, which is 3.3V when connected to the NUCLEO SWD connector.

I don't know what I missed on the design too ...

[Tesla DeLorean]

Things are hard to guess at.

Should try a stand-alone ST-LINK

For Nucleo ST-LINK make sure to disconnect the local target

For L0 parts, try connectivity at 4 MHz or less

Evaluate if you can get to the system loader

Connect NRST to the debug pod, so "Connect Under Reset" is workable when the module powers down.

Built things with the Murata module here and not failed at it.

[Flavio Alves]

Thank you for your fast response.

I tested also on a stand alone ST-Link V2.

And the result is the same.

The set speed for 4 MHz in all cases.

I checked the power pins and they all all with 3.3V :|

What do you mean by system loader?