``` text
+------+ +-----+ +----------+ +----------+ +----+
| User |-------->| Key |------>| Firmware |----->| USB wire |---->| OS |
-+------+ +-----+ +----------+ +----------+ |----+
++------+ +-----+ +----------+ +----------+ +----+
```
This scheme is a very simple view of what's going on, and more details follow
## 2. What the Firmware Sends
-The [HID specification](http://www.usb.org/developers/hidpage/Hut1_12v2.pdf) tells what a keyboard can actually send through USB to have a chance to be properly recognised. This includes a pre-defined list of scancodes which are simple numbers from `0x00` to `0xE7`. The firmware assigns a scancode to each key of the keyboard.
+The [HID specification](https://www.usb.org/sites/default/files/documents/hut1_12v2.pdf) tells what a keyboard can actually send through USB to have a chance to be properly recognised. This includes a pre-defined list of scancodes which are simple numbers from `0x00` to `0xE7`. The firmware assigns a scancode to each key of the keyboard.
-The firmware does not send actually letters or characters, but only scancodes.
-Thus, by modifying the firmware, you only can modify what scancode is sent over
+The firmware does not send actual letters or characters, but only scancodes.
+Thus, by modifying the firmware, you can only modify what scancode is sent over
USB for a given key.
## 3. What the Operating System Does
Once the keycode reaches the operating system, a piece of software has to have
it match an actual character thanks to a keyboard layout. For example, if your
-layout is set to QWERTY, a sample of the matching table is as follow:
+layout is set to QWERTY, a sample of the matching table is as follows:
| keycode | character |
|---------|-----------|
## List of Characters You Can Send
-Putting aside shortcuts, having a limited set of keycodes mapped to a limited layout means that **the list of characters you can assign to a given key only is the ones present in the layout**.
+Putting aside shortcuts, having a limited set of keycodes mapped to a limited layout means that **the list of characters you can assign to a given key are only the ones present in the layout**.
-For example, this means that if you have a QWERTY US layout, and you want to assign 1 key to produce `€` (euro currency symbol), you are unable to do so, because the QWERTY US layout does not have such mapping. You could fix that by using a QWERTY UK layout, or a QWERTY US International.
+For example, this means that if you have a QWERTY US layout, and you want to assign one key to produce `€` (euro currency symbol), you are unable to do so, because the QWERTY US layout does not have such mapping. You could fix that by using a QWERTY UK layout, or a QWERTY US International.
-You may wonder why a keyboard layout containing all of Unicode is not devised then? The limited number of keycode available through USB simply disallow such a thing.
+You may wonder why a keyboard layout containing all of Unicode is not devised then? The limited number of keycodes available through USB simply disallows such a thing.
## How to (Maybe) Enter Unicode Characters
-You can have the firmware send *sequences of keys* to use the [software Unicode Input Method](https://en.wikipedia.org/wiki/Unicode_input#Hexadecimal_code_input) of the target operating system, thus effectively entering characters independently of the layout defined in the OS.
+You can have the firmware send *sequences of keys* to use the [software Unicode Input Method](https://en.wikipedia.org/wiki/Unicode_input#Hexadecimal_input) of the target operating system, thus effectively entering characters independently of the layout defined in the OS.
Yet, it does come with multiple disadvantages:
- - Tied to a specific OS a a time (need recompilation when changing OS);
+ - Tied to a specific OS at a time (need recompilation when changing OS);
- Within a given OS, does not work in all software;
- Limited to a subset of Unicode on some systems.
projects / qmk_firmware.git / blobdiff