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) 6MHz crystal Kyocera(KSS) CX1255CA https://ele.kyocera.com/sites/default/files/assets/static/discontinued/cx1255ca_2013_e.pdf Keyswitch PCB ------------- HC4051 Analog Multiplexer: select a row line. http://www.ti.com/lit/ds/schs122j/schs122j.pdf LS145 BCD Decoder: select a column line. http://www.ti.com/lit/ds/symlink/sn74ls145.pdf BU9831 Non-volatile electronic potentiometer: for calibration? https://www.spezial.com/doc/rohm-a/bu9831.pdf 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 lines are for keyboard signaling. HHKB connector lines: JP Pro2 Pro Function Description TMK pin usage -------------------------------------------------------------------------------------------- 1 Vcc(5V) 5V 1 1 2 Vcc(5V) 5V 2 2 3 Vcc(5V) 5V 3 3 4 TP1684 ~KEY: Low(0) when key is pressed PD7 input(with pullup) 4 4 5 TP1684 HYS: High(1) when key is pressed PB7 output 5 5 6 HC4051 A(bit0)\ PB0 output 6 6 7 HC4051 B(bit1) > select row 0-7 PB1 output 7 7 8 HC4051 C(bit2)/ PB2 output 8 8 9 LS145 A(bit0)\ PB3 output 9 9 10 LS145 B(bit1) > select column 0-7 PB4 output 10 10 11 LS145 C(bit2)/ PB5 output 11 11 12 LS145 ~D(enable) Low(0) enables selected column PB6 output 12 12 13 GND GND 13 13 14 GND GND 15 GND 14 HC4051(Z2) ~Enable of Z2 row0-7 PC6 15 HC4051(Z3) ~Enable of Z3 row8-15 PC7 NOTE: Probably HYS changes threshold for upstroke and makes hysteresis in the result. NOTE: HYS should be given High(1) when previous KEY state is Low(0). NOTE: 1KOhm didn't work as pullup resistor on KEY. AVR internal pullup or 10KOhm resistor was OK. NOTE: JP has two HC4051(Z2,Z3) and line 5, 6 and 7 are connected to both of them. (HHKB_connector.jpg) Keyswitch matrix ---------------- HHKB switch matrix is ghost-free and bounce-free. Pro/Pro2(8x8): 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_ JP(16x8): COL 0 1 2 3 4 5 6 7 ROW --------------------------------------------------------------- 0| ESC TAB LFn LShift LCtrl 1| 4 E MuHKN C D 2| 3 W LAlt X S 3| 1 HHK 4| 5| 5 R V F 6| 2 Q LGui Z A 7| 6 T Space B G 8| 9 I Kana , K 9| 8 U Henkan M J A| 7 Y N H B| 0 O RAlt . L C| BS Right RShift Enter D| \ [ Down Up ] E| - P RFn / ; F| ~ @ Left Ro : Matrix diagram: Pro/Pro2: +-------------------------+-+-+-+-+-+-+-+ Vcc |bias control? - - - - - - - - --- | 3.9K*8 R R R R R R R R | +--------^+ +--------+ - - - - - - - - | | 3| | HC4051 <0-------|-|-|-|-|-|-|-|--|R|-+ | DIL-20 |capa. | <1-------|-|-|-|-|-|-|-|--|R|-+ | TP1684 |sense | <2-------|-|-|-|-|-|-|-|--|R|-+ | 20<------| <3-------|-|-|-|-|-|-|-|--|R|-+ | | | <4-------|-|-|-|-|-|-|-|--|R|-+ | | | <5-------|-|-|-|-|-|-|-|--|R|-+ >5~EN <-+ | <6-------|-|-|-|-|-|-|-|--|R|-+ | 2 4 | | | <7-------|-|-|-|-|-|-|-|--|R|-+ +---V---^-+ | +-^-^-^--+ 0 1 2 3 4 5 6 7 33K*8 KEY HYS | A B C +-----------------+ | | +-^----+ | | | | LS145 | Vcc | | |BU9831| | | | +-^--^--^--^------+ --- | | +------+ | | | A B C D +-------+ | | | | | | | | | | | | 1-3 4 5 6 7 8 9 10 11 12 13-15 Pro | 1-2 3 4 5 6 7 8 9 10 11 12-13 Pro2| +--------------------------------------------------+ | | connector | --- +--------------------------------------------------+ GND JP: +-----------------------------+-+-+-+-+ Vcc |bias control? - - - - - --- | 3.9K*5 R R R R R | +--------^+ +--------+ - - - - - | | 3| | HC4051 <0-----------|-|-|-|-|----|R|-+ | |capa. | Z2 <1-----------|-|-|-|-|----|R|-+ | TP1684 |sense | <2-----------|-|-|-|-|----|R|-+ | 20<---+--| <3-----------|-|-|-|-|----|R|-+ | | | | <4-----------|-|-|-|-|----|R|-+ | | ~En| <5-----------|-|-|-|-|----|R|-+ >5~EN | +----> <6-----------|-|-|-|-|----|R|-+ | 2 4 | | | | A B C <7-----------|-|-|-|-|----|R|-+ +---V---^-+ | | +-^-^-^--+ | | | | | | KEY HYS | | | | | | | | | | | | | | | +--------+ | | | | | | | | | | | HC4051 <8-----------|-|-|-|-|----|R|-+ | | | | | Z3 <9-----------|-|-|-|-|----|R|-+ | | | +--|