GPIO Pins

Memory Mapped I/O registers

The GPIO registers are separated into sections:

• Section 0: 90000000-9000003F
• Section 1: 90000040-9000007F
• Section 2: 90000080-900000BF
• Section 3: 900000C0-900000FF
• Section 5: 90000140-9000017F

Each register is a word, and only bits 0-7 of each are used. There can be up to 40 devices accessed by this setup, each known as a GPIO. Each GPIO is defined by one of the 8 bits in one of the sections. The number of the GPIO is the section number times 8 plus the bit number. Each GPIO has a status bit and can cause interrupts.

Section registers

The following addresses are offsets from the beginning of the GPIO section:

• +00 (R): Masked interrupt status ([+04] & [+08])
• +04 (R): Reads raw interrupt status (directly dependent on the GPIO input) or sticky interrupt status (becomes set when GPIO status changes) depending on bit in [+20]
• +04 (W): Write 1 to the bit to reset the sticky interrupt status.
• +08 (R): Reads current interrupt mask bit.
• +08 (W): Write 1 to the bit to enable interrupt (set mask bit to 1)
• +0C (W): Write 1 to the bit to disable interrupt (set mask bit to 0)

The following addresses should be changed with a read-modify-write pattern so as to not disturb other bits in the register.

• +10 (R/W): Direction (set bit to 0 for output, 1 for input)
• +14 (R/W): GPIO output bit
• +18 (R): Reads GPIO input bit.
• +1C (R/W): Setting bit to 1 will invert raw interrupt status (?)
• +20 (R/W): Setting bit to 1 will use sticky interrupt status in [+04], or setting to 0 will use raw interrupt status.
• +24 (R/W): (?)

Currently known pins

Bit/section number to GPIO pin

	7	6	5	4	3	2	1	0
Section 0	7	6	5	4	3	2	1	0
Section 1	15	14	13	12	11	10	9	8
Section 2	23	22	21	20	19	18	17	16
Section 3	31	30	29	28	27	26	25	24

	Classic	CX
0
1	I2C clock - for communicating with the Touchpad (see Keypads#Touchpad I²C for details)
2	Input bit is 0 if battery door open, 1 if closed
3	I2C data - for communicating with the Touchpad (see Keypads#Touchpad I²C for details)
4
5
6
7
8	Input bit is 0 if Reset Button is pressed
9
10
11
12
13
14
15
16
17
18
19	Input is 0 if WLAN Cradle attached
20
21
22
23	Called LCD_OFF in diags mode
24	Input bit is 1 if a keypad is not plugged in
25
26
27
28
29
30
31

• GPIO 1 (Section 0, bit 1): Touchpad "clock"
• GPIO 2 (Section 0, bit 2): Input bit is 0 if battery door open, 1 if closed (TI-Nspire CAS)
• GPIO 3 (Section 0, bit 3): Touchpad data
• GPIO 8 (Section 1, bit 0): Input bit is 0 if Reset Button is pressed.
• GPIO 19 (Section 2, bit 3): Input is 0 if WLAN Cradle attached
• GPIO 23 (Section 2, bit 7): Called LCD_OFF in diags mode
• GPIO 24 (Section 3, bit 0): Input bit is 1 if a keypad is not plugged in. (TI-Nspire non-CAS only?)