keyboard/hhkb/doc/HHKB.txt

   1 Internal of HHKB pro
   2 =====================
   3 HHKB pro has MCU and some chips on separate two PCBs.
   4
   5 Controller PCB
   6 --------------
   7     M38K07M4    Renesas MCU with USB function
   8                 http://documentation.renesas.com/eng/products/mpumcu/rej03b0192_38k0ds.pdf
   9
  10     (HHKB_controller.jpg)
  11
  12 Keyswitch PCB
  13 -------------
  14     HC4051      Analog Multiplexer: select a row line.
  15                 http://www.alldatasheet.com/datasheet-pdf/pdf/203989/KODENSHI/KK74HC4051A.html
  16     LS145       BCD Decoder: select a column line.
  17                 http://www.alldatasheet.com/datasheet-pdf/pdf/27373/TI/SN74LS145D.html
  18     BU9831      Non-volatile electronic potentiometer: for calibration?
  19                 http://www.alldatasheet.com/datasheet-pdf/pdf/36387/ROHM/BU9831.html
  20     TP1683/4    Capacitive Sensing controller: no datasheet available.
  21
  22     (HHKB_keyswitch.jpg)
  23
  24     Topre original chip?
  25     (HHKB_TP1684.jpg)
  26
  27
  28 Connector Cable
  29 ---------------
  30 Two PCBs are connected by 15 lines(13 in case of Pro2).
  31 Vcc and GND use 3(2) lines each, other 9 lines are for keyboard signaling.
  32
  33     Keyswitch PCB connector                                 Teensy++ pins
  34     -------------------------------------------------------------------------------
  35      1  Vcc(5V)   Not exist on Pro2                         5V
  36      2  Vcc(5V)                                             5V
  37      3  Vcc(5V)                                             5V
  38      4  TP1684    KEY: Low(0) when key pressed              PE6 input(with pullup)
  39      5  TP1684    KEY_PREV: assert previous key state???    PE7 output
  40      6  HC4051    A(bit0) select 8 rows(0 to 7)             PB0 output
  41      7  HC4051    B(bit1)                                   PB1 output
  42      8  HC4051    C(bit2)                                   PB2 output
  43      9  LS145     A(bit0) select 8 columns(0 to 7)          PB3 output
  44     10  LS145     B(bit1)                                   PB4 output
  45     11  LS145     C(bit2)                                   PB5 output
  46     12  LS145     D(enable) Low(0) enable selected column   PB6 output
  47     13  GND                                                 GND
  48     14  GND                                                 GND
  49     15  GND       Not exist on Pro2                         GND
  50
  51     NOTE: guessing pin5(KEY_PREV) may work for hysteresis of capacitive sensing.
  52
  53     (HHKB_connector.jpg)
  54
  55
  56 Keyswitch matrix
  57 ----------------
  58 60 keyswitches in 8*8 matrix. It is ghost-free and bounce-free.
  59
  60       COL 0     1       2       3       4       5       6       7
  61     ROW ---------------------------------------------------------------
  62       0|  2     q       w       s       a       z       x       c
  63       1|  3     4       r       e       d       f       v       b
  64       2|  5     6       y       t       g       h       n       _NONE_
  65       3|  1     Esc     Tab     Control LShift  LAlt    LMeta   Space
  66       4|  7     8       u       i       k       j       m       _NONE_
  67       5|  \     `       Delete  Return  Fn      RShift  RAlt    RMeta
  68       6|  9     0       o       p       ;       l       ,       _NONE_
  69       7|  -     +       ]       [       '       /       .       _NONE_
  70
  71
  72 Matrix diagram:
  73
  74              +-------------------------+-+-+-+-+-+-+-+     Vcc
  75              |bias control?            - - - - - - - -     ---
  76              |                  3.9K*8 R R R R R R R R      |
  77     +--------^+      +--------+        - - - - - - - -      |
  78     |        2|      | HC4051 <0-------|-|-|-|-|-|-|-|--|R|-+
  79     |         |capa. |        <1-------|-|-|-|-|-|-|-|--|R|-+
  80     | TP1684  |sense |        <2-------|-|-|-|-|-|-|-|--|R|-+
  81     |       11<------|        <3-------|-|-|-|-|-|-|-|--|R|-+
  82     |         |      |        <4-------|-|-|-|-|-|-|-|--|R|-+
  83     |         |      |        <5-------|-|-|-|-|-|-|-|--|R|-+
  84     |         <-+    |        <6-------|-|-|-|-|-|-|-|--|R|-+
  85     |   1   4 | |    |        <7-------|-|-|-|-|-|-|-|--|R|-+
  86     +---V---^-+ |    +-^-^-^--+        0 1 2 3 4 5 6 7  33K*8
  87        KEY PREV |      A B C         +-----------------+
  88         |   | +-^----+ | | |         |      LS145      |
  89     Vcc |   | |BU9831| | | |         +-^--^--^--^------+
  90     --- |   | +------+ | | |           A  B  C  D   +------+
  91      |  |   |          | | |           |  |  |  |   |      |
  92     1-3 4   5          6 7 8           9 10 11 12 13-15    |
  93     +--------------------------------------------------+   |
  94     |                connector                         |  ---
  95     +--------------------------------------------------+  GND
  96                     to controller
  97
  98
  99 Signals charts
 100 --------------
 101     While pressing space bar, watched HHKB original controller signals by logic analyzer.
 102     Row and column is looping between 0-7 each for selecting a key.
 103     A key is scaned every about 15ms, so scan rate is 66Hz.
 104
 105     (HHKB_chart1.jpg)
 106
 107     Space bar locate at ROW:3 COL:7. A key is selected by HC4051(C,B,A) and LS145(C,B,A).
 108     Key state can be read on TP1684(4/KEY) while asserting low on LS145(D).
 109
 110     Usage of TP1684(5) is not clear. Controller seemed to output previous key state on this line.
 111     However key state can be read without using this signal.
 112
 113     (HHKB_chart2.jpg)
 114
 115
 116 Matrix scan pseudo code
 117 -----------------------
 118     for (row: 0-7) {
 119         SELECT_ROW(row);        // set HC4051(A,B,C)
 120
 121         for (col: 0-7) {
 122             SELECT_COL(col);    // set LS145(A,B,C)
 123
 124             _delay_us(40);
 125
 126             if (prev_key_state(row, col)) {
 127                 KEY_PREV_ON;
 128             }
 129
 130             _delay_us(7);
 131
 132             ENALBLE_COL();      // set LS145(D) to low
 133
 134             _delay_us(10);
 135
 136             if (KEY == 0) {     // read TP1684(KEY)
 137                 // key pressed
 138             } else {
 139                 // not pressed
 140             }
 141
 142             KEY_PREV_OFF;
 143             UNALBLE_COL();      // set LS145(D) to high
 144
 145             _delay_us(150);
 146         }
 147     }
 148
 149
 150
 151 EOF