Communication protocol for keyboards used from the PC-8801 FH

■ Communication protocol for keyboards used from the PC-8801 FH

■ Pin arrangement

Uses a mini DIN 5 pin connector (there are actually only 3 lines connected).

■Communication protocol

It is a general start-stop synchronization type.
There is only one signal line, and there are no control signals.

Communication speed 20800 bps

Start bit 1

Data bit 12 (LSB first)

Parity bit 1 (Even parity)

Stop bit 1

Communication speed	20800 bps
Start bit	1
Data bit	12 (LSB first)
Parity bit	1 (Even parity)
Stop bit	1

The Row and Data of the key matrix that has changed will be sent as is.
R3 to R0 are Row and D7 to D0 are Data.

Example: When you press the [A] key, 010 10111111 (2:FD) is sent, and when you release it, 010 11111111 (2:FF) is sent.

After sending one datum, there seems to be an interval of about 2.4ms before sending the next one.
The parity bit is set so that the total number of 1s in the data bit and parity bit is an even number.

For compatibility reasons, some keys expanded in FH and later are considered to be pressed at the same time as other (legacy) keys.
In the key matrix in the table below, if there is a notation at the bottom, that key is also pressed.

Row＼Data 0 1 2 3 4 5 6 7

00h 0 1 2 3 4 5 6 7

01h 8 9 * + = , . RETURN

02h @ A B C D E F G

03h H I J K L M N O

04h P Q R S T U V W

05h X Y Z [ \ ] ^ -

06h 0 1 2 3 4 5 6 7

07h 8 9 : ; , . / _

08h HOMECLR ↑ → INSDEL GRPH カナ (Kana) SHIFT CTRL

09h STOP f.1 f.2 f.3 f.4 f.5 SPACE ESC

0Ah TAB ↓ ← HELP COPY - / CAPS

0Bh ROLL UP ROLL DOWN

0Ch f.6
SHIFT, f.1 f.7
SHIFT, f.2 f.8
SHIFT, f.3 f.9
SHIFT, f.4 f.10
SHIFT, f.5 BS
INSDEL INS
SHIFT, INSDEL DEL
INSDEL

0Dh 変換 (Conversion)
SPACE 決定 (Decision)
SPACE PC 全角 (Full-width)

0Eh RETURN(main)
RETURN RETURN (10key)
RETURN SHIFT (Left)
SHIFT SHIFT (Right)
SHIFT
0

The actual keyboard sends data in the following orders:

INS The press/release order is [extended key] [conventional SHIFT] [conventional key]

f.6 to f.10 When pressing, the order is [extended key][conventional SHIFT][conventional key],
when releasing, the order is [extended key][conventional key][conventional SHIFT]

Others The press/release order is [extended key][traditional key]

Example: If you press and release [f.6], (C:FE)(8:BF)(9:FD)(C:FF)(9:FF)(8:FF) will be sent.

Row＼Data	0	1	2	3	4	5	6	7
00h	0	1	2	3	4	5	6	7
01h	8	9	*	+	=	,	.	RETURN
02h	@	A	B	C	D	E	F	G
03h	H	I	J	K	L	M	N	O
04h	P	Q	R	S	T	U	V	W
05h	X	Y	Z	[	\	]	^	-
06h	0	1	2	3	4	5	6	7
07h	8	9	:	;	,	.	/	_
08h	HOMECLR	↑	→	INSDEL	GRPH	カナ (Kana)	SHIFT	CTRL
09h	STOP	f.1	f.2	f.3	f.4	f.5	SPACE	ESC
0Ah	TAB	↓	←	HELP	COPY	-	/	CAPS
0Bh	ROLL UP	ROLL DOWN
0Ch	f.6 SHIFT, f.1	f.7 SHIFT, f.2	f.8 SHIFT, f.3	f.9 SHIFT, f.4	f.10 SHIFT, f.5	BS INSDEL	INS SHIFT, INSDEL	DEL INSDEL
0Dh	変換 (Conversion) SPACE	決定 (Decision) SPACE	PC	全角 (Full-width)
0Eh	RETURN(main) RETURN	RETURN (10key) RETURN	SHIFT (Left) SHIFT	SHIFT (Right) SHIFT		0

INS	The press/release order is [extended key] [conventional SHIFT] [conventional key]
f.6 to f.10	When pressing, the order is [extended key][conventional SHIFT][conventional key], when releasing, the order is [extended key][conventional key][conventional SHIFT]
Others	The press/release order is [extended key][traditional key]

88VA mode has not been investigated yet.

■ Mystery

Bit 7 of Row 0Eh is always 0 ?