USB Protocol

Key maps

Each bit in the 900E0010-900E001F registers represents a key. Only bits 0 to 10 are used in each halfword. The mapping depends on the currently used keypad.

Clickpad keypad map:

If the bit is cleared, the key is being pressed.

offset	bit 0	bit 1	bit 2	bit 3	bit 4	bit 5	bit 6	bit 7	bit 8	bit 9	bit 10
0010	ret	enter	space	(-)	Z	.	Y	0	X	on	theta
0012	,	+	W	3	V	2	U	1	T	e^x	pi
0014	?	-	S	6	R	5	Q	4	P	10^x	EE
0016	:	*	O	9	N	8	M	7	L	x^2	i
0018	"	/	K	tan	J	cos	I	sin	H	^	>
001A	'	cat	G	)	F	(	E	var	D	shift	<
001C	flag	click	C	home	B	menu	A	esc	|	tab
001E	up	u+r	right	r+d	down	d+l	left	l+u	del	ctrl	=

TI-84+ keypad map:

If the bit is cleared, the key is being pressed.

offset	bit 0	bit 1	bit 2	bit 3	bit 4	bit 5	bit 6	bit 7	bit 8	bit 9	bit 10
0010	down	left	right	up
0012	enter	+	-	*	/	^	clear
0014	(-)	3	6	9	)	tan	vars
0016	.	2	5	8	(	cos	prgm	stat
0018	0	1	4	7	,	sin	apps	X
001A	on	sto	ln	log	x^2	x^-1	math	alpha
001C	graph	trace	zoom	wind	y=	2nd	mode	del
001E

Touchpad/CX/CM/CX II keypad map:

If the bit is set, the key is being pressed.

The On/Home button is not visible here (and can not generate a keypad interrupt) but accessible on the Touchpad/CX/CM at bit 4 of 0x900B0028 and on the CX II at bit 8 of 0x90140810. Both are inverted, i.e. 0 = pressed, 1 = not pressed. libndls' on_key_pressed() function handles that for all models.

offset	bit 0	bit 1	bit 2	bit 3	bit 4	bit 5	bit 6	bit 7	bit 8	bit 9	bit 10
0010	ret	enter		(-)	space	Z	Y	0	?!
0012	X	W	V	3	U	T	S	1	pi	trig	10^x
0014	R	Q	P	6	O	N	M	4	EE	x^2
0016	L	K	J	9	I	H	G	7	/	e^x
0018	F	E	D		C	B	A	=	*	^
001A		var	-	)	.	(	5	cat	frac	del	scratch
001C	flag		+	doc	2	menu	8	esc		tab
001E									shift	ctrl	,

Touchpad I²C

Communication with the actual touchpad is done with the I²C protocol.

On the original Touchpad models, the I2C protocol is bitbanged through the GPIO: GPIO 1 is the Serial Clock (SCL) and GPIO 3 is the Serial Data Line (SDA). On the CX and CX II models, there is a dedicated I2C controller for accessing it.

Calculators before the CX II HW rev. AK use the Synaptics protocol, but later versions (indicated by bit 0 of the HW flags) use a custom touchpad and protocol called "CapTIvate".

Synaptics protocol

The touchpad seems to be a TM-603. The linux driver is a good source for documentation.

it responds to messages with address 0x20. A write message consists of the first port to write to, followed by the values to write: the port number auto-increments, so a message of 00 de ad writes de to port 00 and ad to port 01. A read message reads from whatever port was set by the previous write message, so it generally has to be preceded by an empty write to set the port.

A list of some of the touchpad's ports follows. All 16-bit numbers are big-endian.

• Any page:
  • FF: Page number
• Page 04 (default):
  • 00: Contact (usually is 01 if proximity >= 0x2F, 00 otherwise)
  • 01: Proximity
  • 02-03: X position
  • 04-05: Y position
  • 06: relative X
  • 07: relative Y (both refresh on irq)
  • 0A: 1 if touchpad pressed down, 0 if not
  • 0B: Status (reading this clears the low bits)
    • Bit 0 (0x01): Set when proximity is nonzero
    • Bit 1 (0x02): Set when velocity bytes are nonzero
    • Bit 2 (0x04): Set when unknown byte at 08 is nonzero
    • Bit 3 (0x08): Set when pressed byte has changed
    • Bit 6 (0x40): Set when the touchpad is configured
    • Bit 7 (0x80): Set when an error occured
  • E4-E7: Firmware version
• Page 10:
  • 04-05: Maximum X coordinate (0x0918)
  • 06-07: Maximum Y coordinate (0x069B)

CapTIvate protocol

The captivate touchpad seems to use an entirely custom protocol with less capabilities. It has a simpler structure: The first byte is a command byte, then data is either read or written, depending on the command. Unlike the synaptics protocol, multi-byte values are little-endian.

01: Read "WHY_BOTHER_ME"

• Byte 0: 0/Unknown
• Byte 1: Flag byte
  • Bit 0: Set if touchpad pressed
  • Bit 1: Set if touchpad touched
  • Bit 2: Clear if touchpad touched (?)
  • Bit 3: Set if something changed after the last read
• Byte 2+3: X position
• Byte 4+5: Y position

03: Write unknown

The OS writes a single byte here.

06: Read status

• Byte 0: 0/Unknown
• Byte 1: Whether the touchpad is configured
• Byte 2-5: Unknown

07: Read size

• Byte 0: 0/Unknown
• Byte 1: 0/Unknown
• Byte 2+3: Width
• Byte 4+5: Height

08: Read firmware version

   0, 0, 1, 0, 0, 4

0A: Read unknown

Six unknown bytes.

0C: Write unknown

The OS writes a single byte here.

Keypad Connector

The Connector joining the keypads to the nspire itself has a very basic design concept: There are a bunch of GPIO pins, VCC, and GND. The OS memory-maps the pins to the bit chart seen above, using half as input, half as output. The same pins the touchpad uses for its I2C connection are used for buttons on the clickpad.

The pins are as follows: 1. Ground 2. Vcc 3-30. GPIO pins, alternating Column-Row-Column-Row

On the 84+ Pad: Pin 23 = Link port wire 1 Pin 25 = Link port wire 2

The OS is constantly doing iskeypressed() on all the keys, so the pins end up looking like a square wave if read by a 'scope. Input pins only show the wave if one of their buttons is pressed, but output pins show the whole wave regardless.

If you can't envision how the keys actually work yet, this might help: All the buttons have 2 connectors, that get shorted when they are pressed. The bits in the table above represent columns of buttons. It's not layed out perfectly because it has more than 8 buttons per column, so it gets offset strangely. The bits in the offsets (the rows) represent rows of buttons.

The columns are each hooked to one Input pin. The rows are each hooked to one output pin. The calculator turns on One output pin, and looks for any signals on the inputs. If there are any, it records the button that matches the input pin and that column. It then repeats this process for all the other columns, and the iskeypressed() process is complete.

If this doesn't make any sense still, email me (willrandship at gmail dot com) and I'll see if I can help. --William Shipley 05:38, 16 September 2011 (CEST)