How to Update Frsky R9 Receiver Firmware

I. Bootloader

R9Mini/R9MM, R9MX, and R9Slim+ receivers require the ExpressLRS bootloader to be flashed before the ExpressLRS firmware. The R9Slim does not have a bootloader and requires STLink for initial flashing.

Download the appropriate bootloader file for your receiver. These files are as follows:

• R9mm/mini: r9mm_elrs_bl.frk (14kB) or r9mm_no_btn_elrs_bl.frk (14kB) (The no_btn bootloader should only be used if the bind/start button on the receiver is faulty or broken.)
• R9MX: r9mx_elrs_bl.frk (20 KB)
• R9Slim+ (ACCST): r9slim_plus_elrs_bl.frk (14kB)
• R9Slim+ (ACCESS/OTA): r9slim_plus_ota_elrs_bl.frk (18kB)

Copy the relevant file to your transmitter's SD card (you can place it in the FIRMWARE folder for easy access).

Connect the receiver to the transmitter's Smart Port as shown:

Next, flash the .frk file through the flashing options in OpenTX or EdgeTX (it's more convenient if the External RF module setting is set to the correct mode).

1. Open the transmitter's system menu: For transmitters with a dedicated System Key, press the SYS key. For transmitters with only a Menu Key, long press the Menu key.
2. Press the Page Key until you reach the SD-HC Card page.
3. Select the FIRMWARE folder and press Enter.
   
4. Select the bootloader file, then long press the Enter key.
5. Select "Flash external module" and press Enter.
6. After flashing is complete, press Enter to finish the operation.

Important

You only need to flash the Bootloader once. After flashing it into the receiver, you do not need to reflash it with every update. The R9Slim does not have a bootloader. Therefore, you need to flash it first via STLink.

II. No Sync Troubleshooting

Setting the external RF module to PPM mode can help resolve issues.

1. Check if the receiver's LED is lit to confirm the receiver is powered on.
2. Check if you have set Max Bauds to 115200 or 400000, especially when using QX7 or X9D (on OneBit firmware or EdgeTX). If this is the case, restore it to the correct setting and try again.

III. Connecting Receiver

Note that the RX pin on the receiver should be soldered to the TX pad on the flight controller board, and the TX pin on the receiver should be soldered to the RX pad on the flight controller board.

IV. Configuring Flight Controller

To properly configure your flight controller, the following settings apply to INAV, Betaflight, and other flight controller software.
If these settings are incorrect, subsequent steps will not proceed smoothly, and you may encounter issues.
After configuring the flight controller, close its software and disconnect the computer from the flight controller board to refresh the connection and ensure the port is not occupied.

V. Updating Receiver Firmware

3.1 Method 1: Via Passthrough

1. Ensure you have properly completed the receiver wiring and your flight controller is configured. Additionally, ensure the bootloader has been flashed to the R9 receiver (if applicable).

Important

This is an important step to ensure a successful update. If you have not completed these operations, please go back.

2. Disconnect and close your FC Configurator application (Betaflight Configurator, INAV Configurator, etc.).

• If your receiver only powers on via USB connected to the flight controller, disconnect it. Hold the boot button on the receiver (not the FC), then insert the USB. Release the button when the green and red LEDs are blinking alternately.
• If your receiver only powers on with a battery connected to the flight controller, disconnect it. Then disconnect and reconnect the USB data cable to your flight controller. Do not reconnect the battery for now.

3. Launch ExpressLRS Configurator on your computer, ensure the Official Releases tab is active, and select the Released version to flash to the RX module.
   
4. Select the Device Category and Device target that match your hardware.

• Device Category: FrSky 900 MHz
• Device: FrSky R9MM/Mini 900MHz RX
  • FrSky R9MX 900MHz RX
  • FrSky R9 Slim 900MHz RX (if flashed via STLink)
  • FrSky R9 Slim Plus 900MHz RX
  • FrSky R9 Slim Plus OTA 900MHz RX
    

5. Set the Flashing Method to BetaflightPassthrough
   
6. Set the firmware options for the device.

• Regulatory Domain (Required, select the domain appropriate for your location or country)
• Binding Phrase (Optional but highly recommended. Note this phrase as it should be the same on your other devices, otherwise they won't bind or sync)
• Local WiFi Network Credentials (Optional. Will be used when the device enters WiFi mode next).
  

7. Click the Flash button.
   
8. Wait for the process to complete. A green success bar will appear in ExpressLRS Configurator.
   
9. After a few seconds, the LED on the receiver should return to slow-blink LED mode.
   

3.2 Method 2: Via STLink

1. Disconnect the receiver from the flight controller.
2. Connect the receiver to the STLink V2 dongle. Locate the CLK, DIO, 3v3, and Gnd pads and connect them to the corresponding pins on the dongle.
   R9Mini/R9MM:
   
   R9MX:
   
   R9Slim/R9Slim+:
   
3. Launch ExpressLRS Configurator on your computer, ensure the Official Releases tab is active, and select the Released version to flash to the RX module.
   
4. Select the Device Category and Device target that match your hardware.

• Device Category: FrSky 900 MHz
• Device: FrSky R9MM/Mini 900MHz RX
  • FrSky R9MX 900MHz RX
  • FrSky R9 Slim 900MHz RX (if flashed via STLink)
  • FrSky R9 Slim Plus 900MHz RX
  • FrSky R9 Slim Plus OTA 900MHz RX
    

5. Set the Flashing Method to STLink
   
6. Set the firmware options for the device.

• Regulatory Domain (Required, select the domain appropriate for your location or country)
• Binding Phrase (Optional but highly recommended. Note this phrase as it should be the same on your other devices, otherwise they won't bind or sync)
• Local WiFi Network Credentials (Optional. Will be used when the device enters WiFi mode next).
  

7. Click the Flash button.
   
8. Wait for the process to complete. A green success bar will appear in ExpressLRS Configurator.
   
9. After a few seconds, the LED on the receiver should return to slow-blink LED mode.
   
10. Reconnect the receiver to the flight controller.

———— This article is referenced from ExpressLRS Getting Started: https://www.expresslrs.org/quick-start/receivers/r9/#updating-your-receiver-firmware**