10.1
Signal Description
GPIO signals have alternate hardware functions. The following table lists the GPIO pins and their
analog and digital alternate functions. The digital alternate hardware functions are enabled by setting
the appropriate bit in the
GPIO Alternate Function Select (GPIOAFSEL)
and
GPIODEN
registers
and configuring the
PMCx
bit field in the
GPIO Port Control (GPIOPCTL)
register to the numeric
encoding shown in the table below. Analog signals in the table below are also 3.3-V tolerant and
are configured by clearing the
DEN
bit in the
GPIO Digital Enable (GPIODEN)
register. The
AINx
analog signals have internal circuitry to protect them from voltages over V
DD
(up to the maximum
specified in Table 27-1 on page 1818), but analog performance specifications are only guaranteed if
the input signal swing at the I/O pad is kept inside the range 0 V < V
IN
< V
DD
. Note that each pin
must be programmed individually; no type of grouping is implied by the columns in the table. Table
entries that are shaded gray are the default values for the corresponding GPIO pin.
Important:
The table below shows special consideration GPIO pins. Most GPIO pins are configured
as GPIOs and tri-stated by default (
GPIOAFSEL
=0,
GPIODEN
=0,
GPIOPDR
=0,
GPIOPUR
=0, and
GPIOPCTL
=0). Special consideration pins may be programed to a
non-GPIO function or may have special commit controls out of reset. In addition, a
Power-On-Reset (
POR
) returns these GPIO to their original special consideration state.
Table 10-1. GPIO Pins With Special Considerations
GPIOCR
GPIOPCTL
GPIOPUR
GPIOPDR
GPIODEN
GPIOAFSEL
Default Reset
State
GPIO Pins
0
0x1
1
0
1
1
JTAG/SWD
PC[3:0]
0
0x0
0
0
0
0
GPIO
a
PD[7]
0
0x0
0
0
0
0
GPIO
a
PE[7]
a. This pin is configured as a GPIO by default but is locked and can only be reprogrammed by unlocking the
pin in the
GPIOLOCK
register and uncommitting it by setting the
GPIOCR
register.
The GPIO commit control registers provide a layer of protection against accidental
programming of critical hardware signals including the GPIO pins that can function as
JTAG/SWD signals and the
NMI
signal. The commit control process must be followed
for these pins, even if they are programmed as alternate functions other than JTAG/SWD
or NMI; see “Commit Control” on page 752.
Note:
If the device fails initialization during reset, the hardware toggles the
TDO
output
as an indication of failure. Thus, during board layout, designers should not
designate the
TDO
pin as a GPIO in sensitive applications where the possibility
of toggling could affect the design.
Table 10-2. GPIO Pins and Alternate Functions (128TQFP)
Digital Function (GPIOPCTL PMCx Bit Field Encoding)
b
Analog
or
Special
Function
a
Pin
IO
15
14
13
11
8
7
6
5
4
3
2
1
-
-
-
-
-
CAN0Rx
-
-
-
T0CCP0
I2C9SCL
U0Rx
-
33
PA0
-
-
-
-
-
CAN0Tx
-
-
-
T0CCP1
I2C9SDA
U0Tx
-
34
PA1
SSI0Clk
-
-
-
-
-
-
-
-
T1CCP0
I2C8SCL
U4Rx
-
35
PA2
SSI0Fss
-
-
-
-
-
-
-
-
T1CCP1
I2C8SDA
U4Tx
-
36
PA3
SSI0XDAT0
-
-
-
-
-
-
-
-
T2CCP0
I2C7SCL
U3Rx
-
37
PA4
743
June 18, 2014
Texas Instruments-Production Data
Tiva
™
TM4C1294NCPDT Microcontroller