MBED Serial Debugging

The MBED device includes a "USB DISK" interface (to update the firmware) and a "Serial" interface (to debug and communicate with the PC). They are both using the same USB cable that you connect to the MBED (No additional USB/Serial FTDI cable required). However: The "USB DISK" shows up immediately if you connect the MBED, the serial may need an additional driver (on Windows) and a terminal (serial communication program) to use.

MBED Serial driver.

The MBED serial driver is only required for Windows (Mac and Linux have the serial driver installed by default).
See for the howto on the installation.

Serial communication program

a.k.a. "Terminal Program"
See for a list of possible terminal programs. We advise to use putty.


Standard Laos terminal settings: 115200 bps, 8 bits, No parity, 1 stop bit

Tips and Tricks


Sending a "BREAK" via the serial line will reboot the MBED. This is handy if you just copied new firmware to the MBED. This has the same effect as the Physical "Reset" button on the MBED.
Putty will send a "Break" if you press the "CTRL" and "BREAK" key on the keyboard at the same time.


If the debug messages do not line up correctly, check that you have set "Implicit CR in each LF" ON in the Putty "Settings --> Terminal" menu

Using Arduino's serial Monitor

You can also use the Arduino IDE serial monitor.

Updated by peteruithoven over 10 years ago · 2 revisions