The MULTI-Module bootloader enables firmware updates via the USB port and from a compatible radio running OpenTX or erSkyTX.
Some MULTI-Modules ship with a broken or out of date bootloader. If the bootloader is not working correctly or not the correct version you will need to update it.
A No Sync error when attempting to update the MULTI-Module from OpenTX means that the module you are trying to flash does not have the MULTI-Module bootloader installed.
Updating the Bootloader
The MULTI-Module bootloader can be updated in three ways:
Using Flash Multi to run an application which will update the bootloader
Using Flash Multi to write firmware via a USB-to-serial adapter
Using the Arduino IDE to compile and flash firmware via a USB-to-serial adapter
An external USB-to-serial adapter is not required to update the bootloader on a Jumper JP4IN-SE or RadioBoss JP4IN1 module as they have an integrated CP2102 USB-to-serial and can be updated easily via the USB port using Flash Multi.
Flash Multi (BootReloader)
This process is for MULTI-Modules with a 'native' USB port. These modules appear in Device Manager as 'Maple' or 'MULTI-Module' devices.
This process is for MULTI-Modules connected via an external or internal USB-to-serial adapter, such as a CP2102, CH340G, or FTDI adapter. This includes all modules which use the SiLabs CP2102 driver, such as JP4IN1 modules.
Install Flash Multi
Install the necessary drivers
Launch Flash Multi
Connect the MULTI-Module via the USB-to-serial adapter
Select an appropriate firmware file
Ensure the correct COM port is selected
Click Write Module to write the firmware and bootloader to the module
Many modules will require header pins to be soldered in place in order to connect an external USB-to-serial adapter. They will also require a 'BOOT0' jumper in order to be put in flashing mode. See the MULTI-Module Github pages for more details.