IBM 4704 Keyboard
=================
IBM capacitive switch models:
    6019273 Model 100 50-key (grid layout)      http://kishy.dyndns.org/?p=977
    6019284 Model 200 62-key Alpha(60% layout)  http://kishy.dyndns.org/?p=894
    6019303 Model 300 77-key Expanded Alpha     http://kbtalking.cool3c.com/article/23272
    6020218 Model 400 107-key Full key          http://kishy.dyndns.org/?p=980

Alps switch(vintage Green) models:
    5954339 Japanese 102-key    http://deskthority.net/post87127.html#p87127
    6112883 Japanese 102-key    http://geekhack.org/index.php?topic=52888.msg1194489#msg1194489
    6112884 Japanese 102-key    http://geekhack.org/index.php?topic=50437.msg1193047#msg1193047
    6341739 Chinese 102-key     http://geekhack.org/index.php?topic=52888.msg1176566#msg1176566

Resourse
--------
The IBM 4704: lots of pictures and info
http://kishy.dyndns.org/?p=648#more-648 

Brochure:
http://ed-thelen.org/comp-hist/IBM-ProdAnn/4700.pdf



IBM 4704 Keyboard Protocol
==========================
On powering up keyboard sends keyboard ID; A3h for 6019284(62-key), for example.
After that the keyboard enters FC command mode and waits for parameter data from host
so that it doesn't send any scancode until you send 'FF'(End of FC command mode).

    Keyboard                    ID
    -------------------------------
    Model 100 50-key            A2h
    Model 200 62-key            A3h
    Model 300 77-key            A4h
    Model 400 107-key           A5h
    Japanese/Chinese 102-key    A6h


Connector
---------
    Keyboard Plug from front

    DSUB-9
    -------------
    \ N 2 3 4 5 /
     \ N N N N /
      ---------
    2   GND
    3   VCC 5V
    4   DATA
    5   CLOCK
    N   No connection/No pin.


Keyboard to Host
----------------
Data bits are LSB first and Pairty is odd. Clock has around 60us high and 30us low part.

            ____      __   __   __   __   __   __   __   __   __   ________
    Clock       \____/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/
                 ____ ____ ____ ____ ____ ____ ____ ____ ____ ____    
    Data    ____/    X____X____X____X____X____X____X____X____X____X________
                Start   0    1    2    3    4    5    6    7    P  Stop

Start bit:  can be long as 300-350us.
Inhibit:    Pull Data line down to inhibit keyboard to send.
Timing:     Host reads bit while Clock is hi.
Stop bit:   Keyboard pulls down Data line to lo after 9th clock.


Host to Keyboard
----------------
Data bits are LSB first and Pairty is odd. Clock has around 60us high and 30us low part.

            ____        __   __   __   __   __   __   __   __   __   ________
    Clock       \______/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/  \_/
                ^   ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ___
    Data    ____|__/    X____X____X____X____X____X____X____X____X____X   \___
                |  Start   0    1    2    3    4    5    6    7    P   Stop
                Request by host

Start bit:  can be long as 300-350us.
Request:    Host pulls Clock line down to request to send a command.
Timing:     After Request keyboard pull up Data and down Clock line to low for start bit.
            After request host release Clock line once Data line becomes hi.
            Host wirtes a bit while Clock is hi and Keyboard reads while low.
Stop bit:   Host releases or pulls up Data line to hi after 9th clock and waits for keybaord pull down the line to lo.


Scancodes
---------
Keyboard doesn't send Break code for all keys except for Alt by default.

    6019284 62-key:
    ,-----------------------------------------------------------.
    |  `|  1|  2|  3|  4|  5|  6|  7|  8|  9|  0|  -|  =|???|BS |
    |-----------------------------------------------------------|
    |Tab  |  Q|  W|  E|  R|  T|  Y|  U|  I|  O|  P| ￠|  \|  PD2|
    |-----------------------------------------------------------|
    |Ctrl  |  A|  S|  D|  F|  G|  H|  J|  K|  L|  ;|  '| {}| PD3|
    |-----------------------------------------------------------|
    |Shif| <>|  Z|  X|  C|  V|  B|  N|  M|  ,|  ,|  /|???|Shift |
    |-----------------------------------------------------------|
    |Reset|blk|Alt  |         Space             |Alt  |blk|Enter|
    `-----------------------------------------------------------'
    +----------+---------------------+----------+----------+
    |`       00|PD1     04|Caps    20|LShift  30|Reset   31|
    |1       18|q       05|a       21|<>      3E|Rblank  41|
    |2       19|w       06|s       22|z       32|Alt     3F|
    |3       1A|e       13|d       23|x       33|Space   40|
    |4       10|r       14|f       24|c       34|Alt     3F|
    |5       11|t       15|g       25|v       35|Lblank  42|
    |6       12|y       16|h       26|b       36|Enter   2F|
    |7       08|u       17|j       27|n       37|          |
    |8       09|i       01|k       28|m       38|          |
    |9       0A|o       02|l       29|,       39|          |
    |0       0F|p       03|;       2A|.       3A|          |
    |-       1F|￠      1B|'       2B|/       3B|          |
    |=       0D|\       1C|{}      2C|???     3C|          |
    |???     0C|PD2     1D|PD3     2D|RShift  3D|          |
    |BS      0E|          |          |          |          |
    +----------+---------------------+----------+----------+
    Bit7 is 'press flag' which set 1 on press and 0 on release when break code is enabled.

NOTE: When break code is enabled the key sends scancode with setting 7th bit on press
and without it on release. That is, '`' sends 80h on press and 00h on release.


Keyboard command
----------------
Keyboard accepts these commands from host.

        Description                             Entry point
    -----------------------------------------------------------
    FF  Soft Reset                              0008h
    FE  Resend                                  00e8h
    FD  Buzzer(emits a short beep)              00edh
    FC  Set Key Flag                            00f6h
    FB  Soft Reset                              0008h
    FA  Reset                                   0000h
    

Keyboard response
-----------------
Keyobard sends these bytes to host.

        Description                             Entry point
    -----------------------------------------------------------
    FE  Overflow(key event/receive data)        00c5h, 0346h
        Memory test error                       0224h
    FD  Command out of bound                    00d8h
        Key out of bound
    7E  Read/Parity error in receive from host  00bch


Set Key Flag command(FC)
------------------------
After 'Power on Reset' firmware enters this command mode and waits for data from host,
so that you don't need to send 'FC' and it doesn't send any scancode until you send 'FF'.

Data sent from host:

    bit: 7   6 ... 0
         en  |     |
         |   `-----`--- scan code
         `------------- enable bit(0: enable repeat, 1: enable break)

    00-77   Enable repeat(78-7F: invalid scancode)
    80-F7   Enable break(F8-FF: invalid scancode)
    FE      Resend(011ah) no need to use
    FF      End(0114h) exits FC command mode.

Response from keyboard:
    FD      Out of bound - Invalid scancode

Examples:
    To enable break code of all keys.

    FC 80 81 ... F7 FF

