How do you upgrade RN4020 firmware on a customer board?


To be able to upgrade the firmware on the RN4020, you need access to the following pins on RN4020:

  1. RX
  2. TX
  3. GND
  4. CTS
  5. RTS
  6. VCC (Optional if the RN4020 can be powered externally)
  7. WAKE _SW

If you have a microcontroller on the board, please make sure it does not interfere with the UART pins. If it is pre-programmed, you can hold it in reset until the upgrade is complete.
You also need to have a USB to UART bridge. We recommend the MCP2221 Breakout Module.


Make the following connections:

  • RN4020 > USB to UART bridge
  • RX > TX
  • TX > RX
  • CTS > RTS
  • RTS > CTS
  • GND > GND
  • VCC > VCC


Once the correct connections are made, open up a terminal and connect to the RN4020 through the USB to UART bridge you made the connection to. Select the right COM port with 115200 Bd, 8-bit, one stop, no parity and hardware flow control enabled.


Power cycle the RN4020 and it will print CMD on the terminal. Send the following commands to the module:


Send D and make sure the flow control is on by checking features.


Once confirmed, download the RN4020 DFU utility from the RN4020 landing page (under Documents > Software).


Close your terminal, open DFU utility and select right COM port, select the firmware you want to be flashed on RN4020 and click Update.

Do not disconnect the RN4020 while it is upgrading, this may brick RN4020.

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