fixed "security key" (Bediensicherungsbaugruppe) handling

* the keypress events were swallowed due to debouncing
* instead, we process the corresponding bits in the keyboard matrix
  now only after debouncing.
* we now generate a short keypress event (immediately followed by a keyrelease)
  not only when removing, but also when inserting the physical key.
* when removing the key, F18 (in Unimap's geometry, by default mapped to RCTRL)
  is additionally pressed. This can be used to discern removing from inserting.
  In the common case that you own only one physical key, you can remap F18
  to the removal action and F19 (or whatever corresponds to your key) to the
  insertion action.

1 files changed, 6 insertions, 1 deletions

diff --git a/README.md b/README.md
index 516810d..89f9151 100644
--- a/README.md
+++ b/README.md
@@ -12,7 +12,10 @@ while supporting most of its original features and many new features:
 * Full N Key Rollover.
   The original firmware supported only 3-Key Rollover.
 * The security key ("Bediensicherungsbaugruppe") is exposed as a key
-  between F19 and F24.
+  between F18 and F24 (in the Unimap framework).
+  Inserting it will generate a keypress of F19-F24, depending on the "security key"
+  actually used. When removing it, F18 is additionally pressed which is mapped
+  to RCTRL but can be remapped using the Keymap editor as necessary.
 * Supports the [Unimap keymapping framework](https://github.com/tmk/tmk_keyboard/blob/master/tmk_core/doc/unimap.txt)
   which eases adapting the keyboard layout and allows you to edit the keymap without
   recompilation using the online [Keymap editor](http://www.tmk-kbd.com/tmk_keyboard/editor/unimap/).
@@ -116,6 +119,8 @@ Desolder the buzzer's 390R resistor and connect the side *facing away* from it
 to a jumper cable.
 It will connect to pin __FIXME__ of the Teensy.
 
+Desolder the IFFS cable.
+
 Connect the VCC, GND and the control pin of the relay using jumper cables with
 the Teensy.
 The control pin should be connected to PB3 of the Teensy.