129 lines
4.7 KiB
Markdown
129 lines
4.7 KiB
Markdown
# Serial Library
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The serial library #docs
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The **serial library** supports [serial communication](https://en.wikipedia.org/wiki/Serial_port) 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.
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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.
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```
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serial.writeLine("started...")
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input.onButtonPressed(Button.A, () => {
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serial.writeLine("A pressed")
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})
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```
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## How to read the micro:bit's serial output from your computer
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Unfortunately, using the serial library requires quite a bit of a setup.
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### Windows
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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:
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* Follow instructions at https://developer.mbed.org/handbook/Windows-serial-configuration in order to install the device driver
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* Install a terminal emulator; we recommend [Tera Term](https://ttssh2.osdn.jp/index.html.en). At the time of this writing, the latest version is 4.88 and can be downloaded [from here](http://en.osdn.jp/frs/redir.php?m=jaist&f=%2Fttssh2%2F63767%2Fteraterm-4.88.exe). Follow the instructions from the installer.
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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.
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* Hit `File` > `New Connection`
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* Check "Serial"; in the dropdown menu, pick the COM port that says "mbed Serial Port". Hit `Ok`.
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* In the menus, hit `Setup` > `Serial Port` and set the baud rate to `115200`.
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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.
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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.
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### Alternative Windows setup with Putty
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If you prefer another terminal emulator (such as [PuTTY](http://www.putty.org/)), here are some instructions.
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* Open Windows's [Device Manager](https://windows.microsoft.com/en-us/windows/open-device-manager); expand the section called "Ports (COM & LPT)"; write down the com number for "mbed Serial Port" (e.g. COM14)
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* 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.
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* (optional): in the "Terminal" section, check "implicit cr in every lf"
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### Linux
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(Untested).
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* Plug in the micro:bit
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* Open a terminal
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* `dmesg | tail` will show you which `/dev/` node the micro:bit was assigned (e.g. `/dev/ttyUSB0`)
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* Then, do: `screen /dev/ttyUSB0 115200` (install the `screen` program if you don't have it). To exit, run `Ctrl-A` `Ctrl-D`.
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Alternative programs include minicom, etc.
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### Mac OS
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* Plug in the micro:bit
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* Open a terminal
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* `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)
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* `screen /dev/cu.usbmodem1422 115200` will open up the micro:bit's serial output. To exit, hit `Ctrl-A` `Ctrl-D`.
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## Using the serial library in your programs
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If the ``serial`` button is not available, you will need first to add the ``micro:bit serial`` library to your script:
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* tap on `add new`
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* tap on `library`
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* select `micro:bit serial`
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### Writing data
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This is basically what you will use the serial library for: debugging purposes.
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* write a number
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```
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serial.writeNumber(42)
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```
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* write a string
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```
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serial.writeString("hello")
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```
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* write a line of text
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```
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serial.writeLine("this is a line")
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```
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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.
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* write an image
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```
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let img = images.createImage(`
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. . . . .
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. # . # .
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. . . . .
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. . . . .
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# # # # #
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`)
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serial.writeImage(img)
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```
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* write the current screen LED status
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```
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serial.writeScreen()
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```
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### Reading data
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This is useful if you have something connected at the other end. As explained above, this is not yet a scenario.
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* reads a line of text
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```
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let msg = serial.readString()
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```
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