I am working on an economic module to be able to use serial communication with the Sparkfun SAMD21 mini development card. And I have one, the DTR (of my CH340G) do I have to connect it to the reset of my MCU? I mean, to reset the board, do I just have to press the reset button on the module or both (the MCU and the USB / UART module)? I enclose the schematic of how I made the small module, if anyone has suggestions or recommendations, I appreciate them.


It occurred to me to review the diagram of the arduino nano, which has the integrated USB / UART bridge, and from what I see, the DTR connects to the reset of the microcontroller and then to the button.


  • Why would you look at the schematic of the Nano which uses a completely different MCU and bootloader / programming system? You should look at a device that uses the same chip as the one you are using. – Majenko Sep 29 '20 at 14:11
  • i search, but i only found the Arduino Zero, that dont use a USB/UART bridge in this format, that uses a MCU. – Valentino Zaffrani Sep 29 '20 at 14:19
  • the SAMD21 has native USB and Arduino core listens for 1200 baud short connection to invoke a reset to bootloader. nobody wires a USB chip to SAMD21. or a double reset activates the bootloader. what do you want to do with the CH340? do you have an UART bootloader for SAMD? – Juraj Sep 29 '20 at 15:49
  • I was thinking that the D+ and D- on the SAMD21 are only to programm, (like the JTAG on FPGAs). So, i have a full COM connection with that same usb too? – Valentino Zaffrani Sep 29 '20 at 16:42
  • look at Arduino SAMD21 boards schematics. Zero, MKR or Nano 33 IoT – Juraj Sep 29 '20 at 18:23

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