This firmware converts Apple ADB keyboard/mouse protocol to USB, you can use it to plug old ADB keyboard/mouse into modern computer. It works on prebuilt TMK ADB-USB Converter or generic dev board with USB AVR MCU(ATMega32U4/2) like Teensy2.0.
This converter uses AVR's internal pull-up, but it seems to be too weak, in particular when you want to use a long or coiled cable. The external pull-up resistor(1K-10K Ohm) on Data is strongly recommended.(It is almost must!)
How to define the keymap is probably obvious. You can find key symbols in common/keycode.h. And see [doc/keymap.md](../../tmk_core/doc/keymap.md) for more detail.
Many of old ADB keyboards have mechanical push-lock switch for Capslock key and this converter supports the locking Capslock key by default. Use keycode `LCAP` instead of `CAPS` in your keymap in short. See README in top directory for more detail.
If you want to remap Capslock key you will have to remove locking pin or just replace with normal momentary switch. Some keyboards like Apple Adujstable keyboard use firmware-base locking with momentary switch for Capslock and remapping it won't be useful in most cases.
though ADB protocol itself supports it. See tmk_core/protocol/adb.c for more info.
Notes for mouse
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ADB mouse support was added by @mek-apelsin on Apr,2015.
https://github.com/tmk/tmk_keyboard/pull/207
All one-button mouses should be supported.
As of 2019 June, the converter can handle multi-button mice and trackball up to eight buttons if the pointing device supports Apple Extended Mouse protocol. But some devices use their own specific protocol unfortunately and they will work as one-button mouse unless device specific code is added.
Kensington Turbo Mouse 5(#64210) is supported now.