I'm new at STM MCUs and trying to develop a new board based on STM32G070RBT6. I have few questions like reset, program over UART, etc.

[Amad]

1) I've checked multiple schematics for blue pill, black pill, etc., and saw capacitor and resistor on reset button line. I've built a test (pinout) board and without any capacitor or resistor. I can reset it (NRST pin to ground). May this cause a hardware or software fault in the future ? I've checked datasheet and there is only shows 0.1 uF capacitor for just protection. Do I need any other component on NRST line ?

2) I'm using FTDI (also tried CH340G) for UART (via Demonstrator GUI) and unable to connect to board. Connections are correct: RX->TX, TX-RX, GND->GND, VDD->3V3. Tried all possible UART2, 3, 4 and so... Is this board can be able to program over UART or do I have a mistake ?

3) On Bluepill there are Boot0 and Boot1 but 32G070 just have Boot0. I've already figured out I can program with STLink swdio, sclk etc but do I need any resistor like bluepill on Boot0 ? Tried to put a serial resistor like that but in that case I couldn't use STLink.

Regards

[TDK · Accepted solution]

1) No, 0.1uF is all you need, unless you are worried about ESD in which case you may want additional protection. Not having a capacitor will be okay most of the time, but you can get parasitic resets if high frequency signals run close to the NRST pin/trace. On boards you care about, it should have a 0.1uF cap per the design document

https://www.st.com/resource/en/application_note/dm00443870-getting-started-with-stm32g0-series-hardware-development-stmicroelectronics.pdf 

Edit: The design document doesn't actually specify a 0.1uF cap for this chip. Perhaps this chip is different, or perhaps the document is incomplete.

2) Per AN2606, the bootloader on this chip support multiple USART peripherals. You will need to enter bootloader mode first before it will respond.

https://www.st.com/resource/en/application_note/cd00167594-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf

3) You will need to pull BOOT0 low to run user code and high to enter the bootloader. There are many ways to accomplish this. One is having a pulldown in parallel with a momentary switch that pulls it high. There may be some option byte settings which override BOOT pin values.

[Amad]

Thank you @TDK​ , I'll read and try to absorb those documents 🙂

Another question: there is USB connected to PA12, PA11 on STM32F103C8T6. I suppose we can directly program over USB F103. Can I have same future at G070RB ? I've checked pinouts and connectivity but couldn't found it. I just want to be sure.

PS: I don't want to add another IC like F103 or any other AN2606 device - like nucleo64

Thank you again

[TDK]

AN2606 has the answers to those questions.

The STM32F103 does not support a USB (DFU) bootloader.

The STM32G070 also does not support a USB (DFU) bootloader.

You can put a USB to UART chip on the board, or create your own custom bootloader (which will need loaded through SWD or other bootloader approved connection) to support USB natively.

Programming/developing over SWD is going to be much more productive than over an interface like USB or UART which doesn't support debugging.

[Amad]

One more question according to STM32G070RBT6 again;

In the documents sent by TDK, there are 10pf caps at LSE and 20pf caps HSE oscillator. My question is; are these capacitors' values important or not?

[TDK]

You can't just use any capacitor value you want, if that's the question. The value of the caps will depend upon your layout and the selected crystal.

https://www.st.com/resource/en/application_note/cd00221665-oscillator-design-guide-for-stm8afals-stm32-mcus-and-mpus-stmicroelectronics.pdf

[Amad]

I started to hate myself because I really waited too long to start STM family ICs... Thank you very much @TDK​ and STM family

Best Regards