XM1110 usart protocol



I’ve salvaged two XM1110 modules from a pair of radiosondes but I’m not able to communicate with them.

According to the datasheet the modules default to 9600bps and NMEA protocol but I’ve tried virtually all meaning baud rates with no success.

I’ve probed TXO with my oscilloscope and it’s spitting some form of data at about 38400 (guessed) bps which seem to repeat every second.

Is there another protocol the modules can talk? Can’t find it in the datasheet.

Is there a procedure to revert it to factory settings.

Thank you very much.


It actually is 38400 8n1, but it seem to be a binary protocol.

I can issue some commands from the “Series Software User Guide” and the modules acknowledges them, I’ve managed to enable NMEA output but the binary junk is still there.

I can’t find any reference to the binary protocol format in the documentation.

Any help will be appreciated.


Hi, I recently purchased a bunch of XM1110 modules, and have the same issues. Baudrate 38400 (opposite to what the datasheets claim) and some garbled binary code mixed in with the NMEA sentences. I tried to use the commands to change to baudrate, but the module does not respond to them. Sierra responded to the company I got these modules from, that the firmware must be upgraded to their latest version. I found their internet page with recources for the XM1110 and there is a link for the “download agent” which is to be used for flashing new firmware.


But when I click on the link, I only get download agents for MT3333 and MT3339.
Pity that Sierra didn’t reply yet to your question, as it appears to be a ‘known problem’.


Hi allardvanw,

I’ve successfully flashed mines to the last UART enabled firmware using the MT3333 download agent and the glonass tool following the procedure described in the document: AirPrime - GNSS Tool - User Guide, which you can download from: https://source.sierrawireless.com/resources/airprime/tools/airprime_gnss_tool_user_guide/.

As download agent I’ve used the file: MTK_AllInOne_DA_MT3333_MP.bin, which is included in the install directory of the GNSS Tool or you can download it at the sierrawireless website.

For the firmware I’ve used the file: AXN5.1.1_8529_3333_1152.1151100.1.bin, which you can download at: https://source.sierrawireless.com/resources/airprime/software/firmware-xm1110-and-xm1110-dev-kit/. It enables UART and I2C but there are other options in the same page.

Hope this helps and if you need further assistance don’t hesitate to ask.


Hi great, thanks! I was wondering why a MT3333 download agent was presented for a XM1110 product. I will try this later today as I have the rest of the software already up and running. I only needed this download agent but was afraid messing up using a product with a name unrelated to the Xm1110. Confusing …