UM10850
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User manual
Rev. 2.4 — 13 September 2016
89 of 464
NXP Semiconductors
UM10850
Chapter 7: LPC5410x I/O pin configuration (IOCON)
pins. If a peripheral input function is defined as coming from more than one source, the
values will be logically combined, possibly resulting in incorrect peripheral operation.
Therefore care should be taken to avoid this situation.
7.4.2.1 Pin function
The FUNC bits in the IOCON registers can be set to GPIO (typically value 000) or to a
special function. For pins set to GPIO, the DIR registers determine whether the pin is
configured as an input or output (see
). For any special function, the pin
direction is controlled automatically depending on the function. The FIOnDIR registers
have no effect for special functions.
7.4.2.2 Pin mode
The MODE bits in the IOCON register allow the selection of on-chip pull-up or pull-down
resistors for each pin or select the repeater mode.
The possible on-chip resistor configurations are pull-up enabled, pull-down enabled, or no
pull-up/pull-down. The default value is pull-up enabled.
The repeater mode enables the pull-up resistor if the pin is high and enables the
pull-down resistor if the pin is low. This causes the pin to retain its last known state if it is
configured as an input and is not driven externally. Such state retention is not applicable to
the Deep Power-down mode. Repeater mode may typically be used to prevent a pin from
floating (and potentially using significant power if it floats to an indeterminate state) if it is
temporarily not driven.
7.4.2.3 Hysteresis
The input buffer for digital functions has built-in hysteresis. See the appropriate specific
device data sheet for quantitative details.
7.4.2.4 Invert pin
This option is included to avoid having to include an external inverter on an input that is
meant to be the opposite polarity of the external signal.
7.4.2.5 Analog/digital mode
When not in digital mode (DIGIMODE = 0) a pin is in analog mode, some digital pin
functions are disabled and any analog pin functions are enabled. In digital mode
(DIGIMODE = 1), any analog pin functions are disabled and digital pin functions are
enabled. This protects the analog input from voltages outside the range of the analog
power supply and reference that may sometimes be present on digital pins, since they are
typically 5V tolerant. All pin types include this control, even if they do not support any
analog functions.
In order to use a pin that has an ADC input option for that purpose, select GPIO (FUNC
field = 0) and disable the digital pin function (DIGIMODE = 0).
In analog mode, the MODE field should be “Inactive” (00); the INVERT, FILTEROFF, and
OD settings have no effect. For an unconnected pin that has an analog function, keep the
DIGIMODE bit set to 1 (digital mode), and pull-up or pull-down mode selected in the
MODE field.