Accessing the REPL¶
REPL (Read-Evaluate-Print-Loop) allows the micro:bit to read and evaluate code in real-time as you write it.
Accessing the REPL on the micro:bit will require you to:
- Determine the communication port identifier for the micro:bit
- Use a program to establish communication with the device
For versions of Windows before 10 you might need to install the Mbed serial driver, the instructions for which are found here:
Using a serial communication program¶
The Mu Editor has built-in support for REPL and even includes a real-time data plotter. Some other common options are picocom and screen. You will need to install a program and read the appropriate documentation to understand the basics of connecting to a device.
Determining the port¶
The micro:bit will have a port identifier (tty, usb) that can be used by the computer for communicating. Before connecting to the micro:bit we must determine the port identifier.
When you have installed the aforementioned drivers the micro:bit will appear in device-manager as a COM port.
Open Terminal and type
ls /dev/cu.* to see a list of connected serial
devices; one of them will look like
/dev/cu.usbmodem1422 (the exact number
will depend on your computer).
In terminal, type
dmesg | tail which will show which
/dev node the
micro:bit was assigned (e.g.
Communicating with the micro:bit¶
Once you have found the port identifier you can use a serial terminal program to communicate with the micro:bit.
You may wish to use Tera Term, PuTTY, or another program.
- In Tera Term:
- Plug in the micro:bit and open Tera Term
- Select Serial as the port
- Go to Setup -> Serial port. Ensure the Port is the correct COM port.
- Choose a baud rate of
115200, data 8 bits, parity none, stop 1 bit.
- In PuTTY:
- Plug in the micro:bit and open PuTTY
- Switch the Connection Type to Serial
- Ensure the Port is the correct COM port
- Change the baud rate to
- Select ‘Serial’ on the menu on the left, then click ‘Open’
Open Terminal and type
screen /dev/cu.usbmodem1422 115200, replacing
/dev/cu.usbmodem1422 with the port you found earlier. This will open the
micro:bit’s serial output and show all messages received from the device.
To exit, press Ctrl-A then Ctrl-\ and answer Yes to the question. There are
many ways back to a command prompt including Ctrl-A then Ctrl-D, which will
detach screen, but the serial port with still be locked, preventing other
applications from accessing it. You can then restart screen by typing
screen program, type
screen /dev/ttyUSB0 115200, replacing
/dev/ttyUSB0 with the port you found earlier.
To exit, press Ctrl-A then \ and answer Yes to the question. There are many
ways back to a command prompt including Ctrl-A then Ctrl-D, which will detach
screen. All serial output from the micro:bit will still be received by
screen, the serial port will be locked, preventing other applications from
accessing it. You can restart screen by typing
picocom /dev/ttyACM0 -b 115200, again replacing
/dev/ttyACM0 with the port you found earlier.
To exit, press Ctrl-A then Ctrl-Q.