diff --git a/keyboard/hhkb/doc/HHKB_keycodes.txt b/keyboard/hhkb/doc/HHKB_keycodes.txt
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+HHKB keycodes
+=============
+2015/10/03
+Looked into unclear keycodes(usages) of Fn-chording-key on HHKB.
+Followings are usages of Keyboard/Keypad Page(0x07) that HHKB spits out when Fn key is down.
+
+## HHK mode(Off-Off)
+    Key         Usage
+    ------------------------
+    ⌘ / ◇       0x78    Stop
+
+## Lite Ext. mode(On-Off)
+
+
+## Mac mode(Off-On)
+    Key         Usage
+    ------------------------
+    Esc         0x66    Power
+    A           0x81    Volume Down
+    S           0x80    Volume Up
+    D           0x7F    Mute
+    F           0x6F    F20
+    Delete      0x53    Num Lock and Clear
+
+
+## Secret mode(On-On)
+    Key         Usage
+    ------------------------
+    Esc         0x66    Power
+    Q           0x78    Stop
+    W           0x7E    Find
+    E           0x74    Execute
+    R           0x77    Select
+    T           0x76    Menu
+    Y           0x75    Help
+    Z           0x7A    Undo
+    X           0x7B    Cut
+    C           0x7C    Copy
+    V           0x7D    Paste
+    B           0x79    Again
+
+
+## Matrix Key-Mode
+
+
+                Mode
+                -------------------------------
+    Key         HHK     Lite    Mac     Secret  Desc
+    ---------------------------------------------------------------------------------------
+    ⌘ / ◇       0x78    -       -       -       Stop
+    Esc         -       -       0x66    0x66    Power
+    A           -       -       0x81    -       Volume Down
+    S           -       -       0x80    -       Volume Up
+    D           -       -       0x7F    -       Mute
+    F           -       -       0x6F    -       F20
+    Delete      0x2A    0x2A    0x53    0x2A    Num Lock and Clear(0x53)/Backspace(0x2A)
+    Q           -       -       -       0x78    Stop
+    W           -       -       -       0x7E    Find
+    E           -       -       -       0x74    Execute
+    R           -       -       -       0x77    Select
+    T           -       -       -       0x76    Menu
+    Y           -       -       -       0x75    Help
+    Z           -       -       -       0x7A    Undo
+    X           -       -       -       0x7B    Cut
+    C           -       -       -       0x7C    Copy
+    V           -       -       -       0x7D    Paste
+    B           -       -       -       0x79    Again
+
+EOF