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+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.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 Teensy++ pins
+ --------------------------------------------------------------------------------------------
+ 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 pressed PE6 input(with pullup)
+ 4 4 5 TP1684 KEY_PREV: make threshold PE7 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
+ 15 HC4051(Z3) ~Enable of Z3 row8-15
+
+ 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.
+ 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 |
+ +--------^+ +--------+ - - - - - - - - |
+ | 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 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 |
+ +--------^+ +--------+ - - - - - |
+ | | | HC4051 <0-----------|-|-|-|-|----|R|-+
+ | |capa. | Z2 <1-----------|-|-|-|-|----|R|-+
+ | TP1684 |sense | <2-----------|-|-|-|-|----|R|-+
+ | <---+--| <3-----------|-|-|-|-|----|R|-+
+ | | | | <4-----------|-|-|-|-|----|R|-+
+ | | ~En| <5-----------|-|-|-|-|----|R|-+
+ | | +----> <6-----------|-|-|-|-|----|R|-+
+ | | | | | A B C <7-----------|-|-|-|-|----|R|-+
+ +---V---^-+ | | +-^-^-^--+ | | | | | |
+ KEY PREV | | | | | | | | | | |
+ | | | | +--------+ | | | | | |
+ | | | | | HC4051 <8-----------|-|-|-|-|----|R|-+
+ | | | | | Z3 <9-----------|-|-|-|-|----|R|-+
+ | | | +--| <A-----------|-|-|-|-|----|R|-+
+ | | | | <B-----------|-|-|-|-|----|R|-+
+ | | | | <C-----------|-|-|-|-|----|R|-+
+ | | | ~En| <D-----------|-|-|-|-|----|R|-+
+ | | | +-> <E-----------|-|-|-|-|----|R|-+
+ | | | | | A B C <F-----------|-|-|-|-|----|R|-+
+ | | | | +-^-^-^--+ 0 1 2 3 4 5 6 7 33K*8
+ | | | | | | | +-----------------+
+ | | | | | | | | LS145 |
+ Vcc | | | | | | | +-^--^--^--^------+
+ --- | | | | | | | A B C D +-------+
+ | | | | | | | | | | | | | |
+ 1-2 3 4 14 15 5 6 7 8 9 10 11 12-13 |
+ +--------------------------------------------------+ |
+ | connector | ---
+ +--------------------------------------------------+ GND
+
+
+Signals charts
+--------------
+ While pressing space bar, watched HHKB Pro 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).
+
+ (HHKB_chart2.jpg)
+
+
+ Signal of JP:
+
+ 1) Select row
+ rowC ____~~~~____~~~~ 3.8/3.8ms(JP) 7.7/7.7ms(Pro) S2 of HC4051
+ rowB __~~__~~__~~__~~ 1.9/1.9ms(JP) 3.8/3.8ms(Pro) S1 of HC4051
+ rowA _~_~_~_~_~_~_~_~ 1.0/1.0ms(JP) 1.9/1.9ms(Pro) S0 of HC4051
+ 0123456701234567 selected row(Pro)
+ 0123456789ABCDEF selected row(JP)
+ rowEn0 ________~~~~~~~~ 7.7/7.7ms(JP only) ~Enable of Z2 HC4051(JP only)
+ rowEn1 ~~~~~~~~________ 7.7/7.7ms(JP only) ~Enable of Z3 HC4051(JP only)
+
+ 2) Select column
+ colC ____~~~~____~~~~ 550/410us(JP) / us(Pro)
+ colB __~~__~~__~~__~~ 200/210us(JP) 450/460us(Pro)
+ colA _~_~_~_~_~_~_~_~ 100/110us(JP) 220/230us(Pro)
+ 0123456701234567 selected column
+
+ 3) Wait 5us after column select, then set prev, strobe colD to spit out key status and read it.
+ prev _~~~~_____ 20us if previous key state is low
+ colD ~~~__~~~~~ 10us strobe
+ key ~~~____~~~ 22us indicates current state of the key
+
+ NOTE: JP scans twice fast as Pro/Pro2 does. So Pro/Pro2 scans 8x8 matrix in 15.4ms while JP scans 16x8 in that time.
+
+
+
+EOF
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