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Fix grammar, typos, and the link to HID specification

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Christoffer Holmberg 2018-10-17 21:54:37 +03:00 committed by Drashna Jaelre
parent 397d404ce0
commit d08f9cb6e4
1 changed files with 7 additions and 7 deletions
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14
docs/how_keyboards_work.md
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@ -27,17 +27,17 @@ This usually happens with a periodic scan of key presses. This speed often is li
## 2. What the Firmware Sends ## 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. The firmware does not send actual letters or characters, but only scancodes.
Thus, by modifying the firmware, you only can modify what scancode is sent over Thus, by modifying the firmware, you can only modify what scancode is sent over
USB for a given key. USB for a given key.
## 3. What the Operating System Does ## 3. What the Operating System Does
Once the keycode reaches the operating system, a piece of software has to have 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 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 | | keycode | character |
|---------|-----------| |---------|-----------|
@ -55,11 +55,11 @@ As the layout is generally fixed (unless you create your own), the firmware can
## List of Characters You Can Send ## 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 ## How to (Maybe) Enter Unicode Characters