Keyboard Layout - peterw8102/Z80-Retro GitHub Wiki

The Omega MSX keyboard is a fairly simple matrix. There are 9 rows, each row contains 8 switches. The processor can read the state of all switches in one row by writing a row number (0-9) to bits 0-3 of port C4h (which is latched) and then reading the value of the 8 switches by reading from port C4h. The following tale shows the position of each of the keys for each row:

Row	Col 7	Col 6	Col 5	Col 4	Col 3	Col 2	Col 1	Col 0
0	7	6	5	4	3	2	1	0
1	;	]	[	\	=	-	9	8
2	b	a	MENU	/	.	,	`	'
3	j	i	h	g	f	e	d	c
4	r	q	p	o	n	m	l	k
5	z	y	x	w	v	u	t	s
6	F3	F2	F1	FN1	LOCK	OPT	CTRL	SHIFT
7	CR	FN2	BS	PGDN	TAB	ESC	F5	F4
8	RIGHT	DOWN	UP	LEFT	DEL	HOME	PGUP	SPC

Col n represents bit n in the value polled back from inout fort C4h.

A pressed key in this matrix is represented by a '0' in the relevant bit in the row value. If no keys are pressed in a polled row then 0xFF is returned.