I'm using an RN-42 Bluetooth module connected to the serial port of a PIC microcontroller.

The Bluetooth module works great and I'm able to send and receive data but when I send a BREAK (hold TX line to 0) from PC through Bluetooth the RN-42 seems not receive it and the TX line continue to stay at high level.

The data path is the following:

PC -> Bluetooth Dongle -> RN-42 Bluetooth module -> PIC Microcontroller

What could be the cause of this problem? Is this problem common to all Bluetooth modules?

  • \$\begingroup\$ Can you put this into schematics or show some code? This is a bit too opaque for me to really understand your problem. \$\endgroup\$
    – user36129
    Aug 8, 2013 at 13:03
  • \$\begingroup\$ I edited the question. \$\endgroup\$
    – Oceanic815
    Aug 8, 2013 at 17:07

1 Answer 1


Looking at the RN-42 Advanced User Manual the only mention of a hardware break appears to be on page 20 for the SB set break command. That only sends a break to the local serial port but you may be able to use the remote configuration to send the set break command from the PC end of things. That won't be transparent however so you'll need codes changes to the PC application.

I couldn't find any references to how Bluetooth SPP (Serial Port Profile) devices should handle hardware breaks although it not getting passed through wouldn't really surprise me. Many legacy devices used the hardware break in different ways and I believe most Hayes style PSTN modems wouldn't pass it through either.

Because you're using a microcontroller personally I'd make my own escape sequence to indicate that the break should be set for a certain period. That way it will remain portable if you ever want to change Bluetooth transceivers at either end.

  • \$\begingroup\$ Thanks for the reply. I tried the SB command but the module returns "ERR", however this command allows to send only a 37 mS break and not a continous break. Unfortunately I need to change the Microchip bootloader code since the Bluetooth SPP doesn't support breaks. \$\endgroup\$
    – Oceanic815
    Aug 10, 2013 at 8:17

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