86: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.

See also TI-83 Plus Port 01, which is identical apart from the key labels & the lack of battery level detection.

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.
• Bit 0 will also read as 0 if groups 0-2 are all selected & the battery level is low.

Write Values

• FFh : Reset the keypad. This unselects all groups and resets the keypad state.
• F8h : Check battery level. This also selects keypad groups 0-2 for monitoring.
• 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 0, otherwise it reads 1 (active-low).

Key Map

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		F5
1	(FD)	LEFT	+	3	2	1	STO	F4
2	(FB)	RIGHT	-	6	5	4	,	F3
3	(F7)	UP	*	9	8	7	x2	F2
4	(EF)		/	)	(	EE	LN	F1
5	(DF)		^	TAN	COS	SIN	LOG	2nd
6	(BF)		CLEAR	CUSTOM	PRGM	TABLE	GRAPH	EXIT
7	(7F)				DEL	x-VAR	ALPHA	MORE

• 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 through Port 03, bit 3.

Comments

• The OS delays about 1400 cycles (100 iterations of a tight DJNZ loop) when checking the battery level at startup, which is much longer than used to test if keys are pressed.
• Bit 0 will be 0 when testing the battery level if the warning message would appear. However, because it is still also wired to the keypad, holding any of DOWN, ENTER, or (-) when turning the calculator on will also cause the warning message to appear.