Internal of HHKB pro
=====================
HHKB pro has MCU and some chips on separate two PCBs.
Controller PCB
--------------
M38K07M4 Renesas MCU with USB function
http://documentation.renesas.com/eng/products/mpumcu/rej03b0192_38k0ds.pdf
(HHKB_controller.jpg)
Keyswitch PCB
-------------
HC4051 Analog Multiplexer: select a row line.
http://www.alldatasheet.com/datasheet-pdf/pdf/203989/KODENSHI/KK74HC4051A.html
LS145 BCD Decoder: select a column line.
http://www.alldatasheet.com/datasheet-pdf/pdf/27373/TI/SN74LS145D.html
BU9831 Non-volatile electronic potentiometer: for calibration?
http://www.alldatasheet.com/datasheet-pdf/pdf/36387/ROHM/BU9831.html
TP1683/4 Capacitive Sensing controller: no datasheet available.
(HHKB_keyswitch.jpg)
Topre original chip?
(HHKB_TP1684.jpg)
Connector Cable
---------------
Two PCBs are connected by 15 lines(13 in case of Pro2).
Vcc and GND use 3(2) lines each, other 9 lines are for keyboard signaling.
Keyswitch connector
pro pro2 Description Teensy++ pins
--------------------------------------------------------------------------------------------
1 Vcc(5V) Not exist on Pro2 5V
2 1 Vcc(5V) 5V
3 2 Vcc(5V) 5V
4 3 TP1684 KEY: Low(0) when key pressed PE6 input(with pullup)
5 4 TP1684 KEY_PREV: make threshold PE7 output
6 5 HC4051 A(bit0)\ PB0 output
7 6 HC4051 B(bit1) > select row(0 to 7) PB1 output
8 7 HC4051 C(bit2)/ PB2 output
9 8 LS145 A(bit0)\ PB3 output
10 9 LS145 B(bit1) > select column(0 to 7) PB4 output
11 10 LS145 C(bit2)/ PB5 output
12 11 LS145 D(enable) Low(0) enables selected column PB6 output
13 12 GND GND
14 13 GND GND
15 GND Not exist on Pro2 GND
NOTE: guessing pin5(KEY_PREV) may work for hysteresis of capacitive sensing.
NOTE: 1KOhm didn't work as pullup resistor on KEY. AVR internal pullup or 10KOhm resistor was OK.
(HHKB_connector.jpg)
Keyswitch matrix
----------------
60 keyswitches in 8*8 matrix. It is ghost-free and bounce-free.
COL 0 1 2 3 4 5 6 7
ROW ---------------------------------------------------------------
0| 2 q w s a z x c
1| 3 4 r e d f v b
2| 5 6 y t g h n _NONE_
3| 1 Esc Tab Control LShift LAlt LMeta Space
4| 7 8 u i k j m _NONE_
5| \ ` Delete Return Fn RShift RAlt RMeta
6| 9 0 o p ; l , _NONE_
7| - + ] [ ' / . _NONE_
Matrix diagram:
+-------------------------+-+-+-+-+-+-+-+ Vcc
|bias control? - - - - - - - - ---
| 3.9K*8 R R R R R R R R |
+--------^+ +--------+ - - - - - - - - |
| 2| | HC4051 <0-------|-|-|-|-|-|-|-|--|R|-+
| |capa. | <1-------|-|-|-|-|-|-|-|--|R|-+
| TP1684 |sense | <2-------|-|-|-|-|-|-|-|--|R|-+
| 11<------| <3-------|-|-|-|-|-|-|-|--|R|-+
| | | <4-------|-|-|-|-|-|-|-|--|R|-+
| | | <5-------|-|-|-|-|-|-|-|--|R|-+
| <-+ | <6-------|-|-|-|-|-|-|-|--|R|-+
| 1 4 | | | <7-------|-|-|-|-|-|-|-|--|R|-+
+---V---^-+ | +-^-^-^--+ 0 1 2 3 4 5 6 7 33K*8
KEY PREV | A B C +-----------------+
| | +-^----+ | | | | LS145 |
Vcc | | |BU9831| | | | +-^--^--^--^------+
--- | | +------+ | | | A B C D +------+
| | | | | | | | | | | |
1-3 4 5 6 7 8 9 10 11 12 13-15 |
+--------------------------------------------------+ |
| connector | ---
+--------------------------------------------------+ GND
to controller
Signals charts
--------------
While pressing space bar, watched HHKB original controller signals by logic analyzer.
Row and column is looping between 0-7 each for selecting a key.
A key is scaned every about 15ms, so scan rate is 66Hz.
(HHKB_chart1.jpg)
Space bar locate at ROW:3 COL:7. A key is selected by HC4051(C,B,A) and LS145(C,B,A).
Key state can be read on TP1684(4/KEY) while asserting low on LS145(D).
Usage of TP1684(5) is not clear. Controller seemed to output previous key state on this line.
However key state can be read without using this signal.
(HHKB_chart2.jpg)
Matrix scan pseudo code
-----------------------
for (row: 0-7) {
SELECT_ROW(row); // set HC4051(A,B,C)
for (col: 0-7) {
SELECT_COL(col); // set LS145(A,B,C)
_delay_us(40);
if (prev_key_state(row, col)) {
KEY_PREV_ON;
}
_delay_us(7);
ENALBLE_COL(); // set LS145(D) to low
_delay_us(10);
if (KEY == 0) { // read TP1684(KEY)
// key pressed
} else {
// not pressed
}
KEY_PREV_OFF;
UNALBLE_COL(); // set LS145(D) to high
_delay_us(150);
}
}
EOF