This site is no longer being updated. For all the latest on BBC micro:bit go to microbit.org.
The serial library supports serial communication between the BBC micro:bit and another computer. Basically, this allows you to send data from the micro:bit to your own computer. This is very useful for debugging purposes: you can add write line statements in your code and see them display on your computer as the program executes.
The code below shows a simple script that sends a line when the BBC micro:bit starts and another line each time the button A is pressed.
serial → write line("started...")
input → on button pressed(A)do
serial → write line("A pressed")
How to read the micro:bit's serial output from your computer
Unfortunately, using the serial library requires quite a bit of a setup.
You must install a device driver (for the computer to recognize the serial interface of the micro:bit); then, you must also install a terminal emulator (which is going to connect to the micro:bit and read its output). Here's how to do it:
Install a terminal emulator; we recommend Tera Term. At the time of this writing, the latest version is 4.88 and can be downloaded from here. Follow the instructions from the installer.
Once both the driver and the terminal emulator are installed, plug in the micro:bit and wait until the device is fully setup. Then, open TeraTerm.
Hit File > New Connection
Check "Serial"; in the dropdown menu, pick the COM port that says "mbed Serial Port". Hit Ok.
In the menus, hit Setup > Serial Port and set the baud rate to 115200.
You should be good. Feel free to hit Setup > Save Setup in the menus to erase the default configuration file with a new one so that you don't have to type in the settings again.
Please note that Windows will assign you a different COM port if you plug in another micro:bit. If you're juggling between micro:bits, you'll have to change the COM port every time.
Alternative Windows setup with Putty
If you prefer another terminal emulator (such as PuTTY), here are some instructions.
Open Windows's Device Manager; expand the section called "Ports (COM & LPT)"; write down the com number for "mbed Serial Port" (e.g. COM14)
Open PuTTY; on the main screen, use the following settings: Serial / COM14 / 115200. Replace COM14 with the COM port number you wrote down previously. Feel free to type in a name and hit "Save" to remember this configuration.
(optional): in the "Terminal" section, check "implicit cr in every lf"
Plug in the micro:bit
Open a terminal
dmesg | tail will show you which /dev/ node the micro:bit was assigned (e.g. /dev/ttyUSB0)
Then, do: screen /dev/ttyUSB0 115200 (install the screen program if you don't have it). To exit, run Ctrl-ACtrl-D.
Alternative programs include minicom, etc.
Plug in the micro:bit
Open a terminal
ls /dev/cu.* will return to you a list of serial devices; one of them will look like /dev/cu.usbmodem1422 (the exact number depends on your computer)
screen /dev/cu.usbmodem1422 115200 will open up the micro:bit's serial output. To exit, hit Ctrl-ACtrl-D.
Using the serial library in your programs
If the serial button is not available, you will need first to add the micro:bit serial library to your script:
tap on add new
tap on library
select micro:bit serial
This is basically what you will use the serial library for: debugging purposes.
write a number
serial → write number(42)
write a string
serial → write string("hello")
write a line of text
serial → write line("this is a line")
Theoretically, you can dump more sophisticated data and then read it back in the event that two micro:bits should be connected to each other over serial. We have not tested this scenario yet as we have yet to expose functionality that allows re-routing the serial ports to the edge connector.
write an image
var img := image → create image()
serial → write image(img)
write the current screen LED status
serial → write screen
This is useful if you have something connected at the other end. As explained above, this is not yet a scenario.