83Plus:Ports:01

Synopsis

Port Number: 01h

Function: Keyboard Port

This port reads key presses from the keypad. The keypad is divided into a series of groups.

Read Values

• Bits are set according whether corresponding keys from selected groups are pressed. Groups are selected through writing to the port. A pressed key reads a 0 bit. An unpressed key reads a 1 bit. The port reads FF after a reset (write FF).

Write Values

• $FF : Reset the keypad. This unselects all groups and resets the keypad state.
• Anything else : Any 0 bit adds the corresponding group to the list of monitored groups. When a key in a monitored group is pressed, the corresponding key bit reads 1.

Comments

The key map is laid out as follows:

	Group Bit	0	1	2	3	4	5	6	7
	Group Mask	FE	FD	FB	F7	EF	DF	BF	7F
Key Bit	(Mask)
0	(FE)	DOWN	ENTER	(-)	.	0		GRAPH
1	(FD)	LEFT	+	3	2	1	STO	TRACE
2	(FB)	RIGHT	-	6	5	4	LN	ZOOM
3	(F7)	UP	*	9	8	7	LOG	WIND
4	(EF)		/	)	(	,	x2	Y=
5	(DF)		^	TAN	COS	SIN	x-1	2nd
6	(BF)		CLEAR	VARS	PRGM	APPS	MATH	MODE
7	(7F)				STAT	X,T,θ,n	ALPHA	DEL

• Note: Group FB Key FE is NEGATE, not to be confused with SUBTRACT.
• Note: Group DF Key FE would be ON, but the ON key is tested elsewhere (a "special case" key - after all, it is the ON key).
• Note: Group EF Key BF (APPS) is called MATRIX on the TI-83.

Example

ld a, 0FFh ;Reset the keypad.
out (1), a
ld a, 0FEh ;Select group 0.
out (1), a
in a, (1) ;Test for keys.
and 0FDh ;Test for Left Arrow key by making A 0 if left was pressed.
call z, LeftArrowPressed ;If 0 then left was pressed.
ld a, 0FFh ;Reset the keypad.
out (1), a