9.1.1 Pin’s pull-up/down and open-drain
All pins have all pull-ups, pull-downs, and inputs turned off at reset except
PIO0_2
,
PIO0_5
,
PIO0_11
,
PIO0_12
,
PIO0_13
, and
PIO0_14
pins. This prevents power loss through pins prior to software configuration. Due to special pin functions, some pins have
a different reset configuration.
PIO0_5
and
PIO0_12
pins have internal pull-up enabled by default, and
PIO0_2
and
PIO0_11
have
internal pull-down enabled by default.
PIO0_13
and
PIO0_14
are true open drain pins.
9.1.2 ADC pins
Some functions, such as ADC or comparator inputs, are available only on specific pins when digital functions are disabled on those
pins. By default, the GPIO function is selected except on pins
PIO0_11
and
PIO0_12
, which are the serial wire debug pins. This
allows debug to operate through reset.
9.1.3 Wakeup pins
The external reset pin or three wake-up pins can trigger a wake-up from deep power-down mode. For the wake-up pins, do not
assign any function to this pin if it will be used as a wake-up input when using deep power-down mode. If not in deep power-down
mode, a function can be assigned to this pin. If the pin is used for wake-up, it should be pulled HIGH externally before entering
deep power-down mode. A LOW-going pulse as short as 50 ns causes the chip to exit deep power-down mode wakes up the part.
9.1.4 JTAG function pins
The JTAG functions, TRST, TCK, TMS, TDI, and TDO, are selected on pins,
PIO0_2
to
PIO0_6
, by hardware
when the part is in boundary scan mode. The JTAG functions cannot be used for debug mode.
NOTE
9.2 Termination of unused pins
shows how to terminate pins that are not used in the application. In many cases, unused pins should be connected
externally or configured correctly by software to minimize the overall power consumption of the part.
Unused pins with GPIO function should be configured as outputs set to LOW with their internal pull-up disabled. To configure a
GPIO pin as output and drive it LOW, select the GPIO function in the IOCON register, select output in the GPIO DIR register, and
write a 0 to the GPIO PORT register for that pin. Disable the pull-up in the pin’s IOCON register.
In addition, it is recommended to configure all GPIO pins that are not bonded out on smaller packages as outputs driven LOW with
their internal pull-up disabled.
Table 12. Termination of unused pins
Pin
Default state
Recommended termination of unused pins
RESET
Input, pull-up
Can be left unconnected if the application does not use it.
All PIOn_m
(not open-drain)
Input, pull-up
Can be left unconnected if driven LOW and configured as GPIO output with
pull-up or pull-down disabled by software.
PIOn_m
(I2C open-drain)
Inactive
No pull-up or down
Can be left unconnected if driven LOW and configured as GPIO output
by software.
XTAL32K_P
—
Connect to ground. When grounded, the RTC oscillator is disabled.
XTAL32K_N
—
Can be left unconnected.
VREFP
—
Tie to VBAT_DCDC
Table continues on the next page...
NXP Semiconductors
Recommendations
Hardware Design Guidelines for LPC55(S)xx Microcontrollers, Rev. 0, 30 October 2020
Application Note
17 / 24
