BBC Keyboard Table
                                 ==================

 Low-level keyboard codes before being translated by Shift, Ctrl, Caps, ShiftLock.

+==+====+====+====+====+====+====+====+====+====+====+====+====+====+====+====+====+
|  | x0 | x1 | x2 | x3 | x4 | x5 | x6 | x7 | x8 | x9 | xA | xB | xC | xD | xE | xF |
+==+====+====+====+====+====+====+====+====+====+====+====+====+====+====+====+====+
|0x|TAB |CAPS|SLCK|    |    |    |    |    |    |    |    |    |    |RETN|    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|1x|    |    |    |    |    |    |    |    |    |    |    |ESC |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|2x|SPC |    |    |    |    |    |    |    |    |    |    |    | ,  | -  | .  | /  |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|3x| 0  | 1  | 2  | 3  | 4  | 5  | 6  | 7  | 8  | 9  | :  | ;  |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|4x| @  |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|5x|    |    |    |    |    |    |    |    |    |    |    | [  | \  | ]  | ^  | _  |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|6x|    | a  | b  | c  | d  | e  | f  | g  | h  | i  | j  | k  | l  | m  | n  | o  |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|7x| p  | q  | r  | s  | t  | u  | v  | w  | x  | y  | z  |    |    |    |    |DEL |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|8x| F0 | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | F9 |    |Copy| <- | -> |Down| Up |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|9x|    |    |    |    |    |    |    |    |    |    |    |    |    |KRet|    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Ax|    |    |    | K# |    |    |    |    |    |    | K* | K+ | K, | K- | K. | K/ |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Bx| K0 | K1 | K2 | K3 | K4 | K5 | K6 | K7 | K8 | K9 |    |    |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Cx|    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Dx|    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Ex|    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
|Fx|    |    |    |    |    |    |    |    |    |    |    |    |    |    |    |KDel|
+--+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+

 &00     translated to the current TAB character code
 &01     toggles Caps Lock status (Compact: Extend key)
 &02     toggles Shift Lock status
 &90-&9F added to keypad offset minus &C0 (ie &9D defaults to &0D)
 &A0+    added to keypad offset minus &B0 (ie &B0 defaults to '0')

On the Master Compact, Ctrl-Shift-Extend sets bit 7 on the next keypress and inserts
NULL,key in the keyboard buffer, unless cancelled by the Escape key.