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 connector
  34     pro  pro2           Description                               Teensy++ pins
  35     --------------------------------------------------------------------------------------------
  36      1       Vcc(5V)    Not exist on Pro2                         5V
  37      2   1   Vcc(5V)                                              5V
  38      3   2   Vcc(5V)                                              5V
  39      4   3   TP1684     KEY: Low(0) when key pressed              PE6 input(with pullup)
  40      5   4   TP1684     KEY_PREV: make threshold                  PE7 output
  41      6   5   HC4051     A(bit0)\                                  PB0 output
  42      7   6   HC4051     B(bit1) > select row(0 to 7)              PB1 output
  43      8   7   HC4051     C(bit2)/                                  PB2 output
  44      9   8   LS145      A(bit0)\                                  PB3 output
  45     10   9   LS145      B(bit1) > select column(0 to 7)           PB4 output
  46     11  10   LS145      C(bit2)/                                  PB5 output
  47     12  11   LS145      D(enable) Low(0) enables selected column  PB6 output
  48     13  12   GND                                                  GND
  49     14  13   GND                                                  GND
  50     15       GND        Not exist on Pro2                         GND
  51
  52     NOTE: guessing pin5(KEY_PREV) may work for hysteresis of capacitive sensing.
  53     NOTE: 1KOhm didn't work as pullup resistor on KEY. AVR internal pullup or 10KOhm resistor was OK.
  54
  55     (HHKB_connector.jpg)
  56
  57
  58 Keyswitch matrix
  59 ----------------
  60 60 keyswitches in 8*8 matrix. It is ghost-free and bounce-free.
  61
  62       COL 0     1       2       3       4       5       6       7
  63     ROW ---------------------------------------------------------------
  64       0|  2     q       w       s       a       z       x       c
  65       1|  3     4       r       e       d       f       v       b
  66       2|  5     6       y       t       g       h       n       _NONE_
  67       3|  1     Esc     Tab     Control LShift  LAlt    LMeta   Space
  68       4|  7     8       u       i       k       j       m       _NONE_
  69       5|  \     `       Delete  Return  Fn      RShift  RAlt    RMeta
  70       6|  9     0       o       p       ;       l       ,       _NONE_
  71       7|  -     +       ]       [       '       /       .       _NONE_
  72
  73
  74 Matrix diagram:
  75
  76              +-------------------------+-+-+-+-+-+-+-+     Vcc
  77              |bias control?            - - - - - - - -     ---
  78              |                  3.9K*8 R R R R R R R R      |
  79     +--------^+      +--------+        - - - - - - - -      |
  80     |        2|      | HC4051 <0-------|-|-|-|-|-|-|-|--|R|-+
  81     |         |capa. |        <1-------|-|-|-|-|-|-|-|--|R|-+
  82     | TP1684  |sense |        <2-------|-|-|-|-|-|-|-|--|R|-+
  83     |       11<------|        <3-------|-|-|-|-|-|-|-|--|R|-+
  84     |         |      |        <4-------|-|-|-|-|-|-|-|--|R|-+
  85     |         |      |        <5-------|-|-|-|-|-|-|-|--|R|-+
  86     |         <-+    |        <6-------|-|-|-|-|-|-|-|--|R|-+
  87     |   1   4 | |    |        <7-------|-|-|-|-|-|-|-|--|R|-+
  88     +---V---^-+ |    +-^-^-^--+        0 1 2 3 4 5 6 7  33K*8
  89        KEY PREV |      A B C         +-----------------+
  90         |   | +-^----+ | | |         |      LS145      |
  91     Vcc |   | |BU9831| | | |         +-^--^--^--^------+
  92     --- |   | +------+ | | |           A  B  C  D   +------+
  93      |  |   |          | | |           |  |  |  |   |      |
  94     1-3 4   5          6 7 8           9 10 11 12 13-15    |
  95     +--------------------------------------------------+   |
  96     |                connector                         |  ---
  97     +--------------------------------------------------+  GND
  98                     to controller
  99
 100
 101 Signals charts
 102 --------------
 103     While pressing space bar, watched HHKB original controller signals by logic analyzer.
 104     Row and column is looping between 0-7 each for selecting a key.
 105     A key is scaned every about 15ms, so scan rate is 66Hz.
 106
 107     (HHKB_chart1.jpg)
 108
 109     Space bar locate at ROW:3 COL:7. A key is selected by HC4051(C,B,A) and LS145(C,B,A).
 110     Key state can be read on TP1684(4/KEY) while asserting low on LS145(D).
 111
 112     Usage of TP1684(5) is not clear. Controller seemed to output previous key state on this line.
 113     However key state can be read without using this signal.
 114
 115     (HHKB_chart2.jpg)
 116
 117
 118 Matrix scan pseudo code
 119 -----------------------
 120     for (row: 0-7) {
 121         SELECT_ROW(row);        // set HC4051(A,B,C)
 122
 123         for (col: 0-7) {
 124             SELECT_COL(col);    // set LS145(A,B,C)
 125
 126             _delay_us(40);
 127
 128             if (prev_key_state(row, col)) {
 129                 KEY_PREV_ON;
 130             }
 131
 132             _delay_us(7);
 133
 134             ENALBLE_COL();      // set LS145(D) to low
 135
 136             _delay_us(10);
 137
 138             if (KEY == 0) {     // read TP1684(KEY)
 139                 // key pressed
 140             } else {
 141                 // not pressed
 142             }
 143
 144             KEY_PREV_OFF;
 145             UNALBLE_COL();      // set LS145(D) to high
 146
 147             _delay_us(150);
 148         }
 149     }
 150
 151
 152
 153 EOF