UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
147 of 515
NXP Semiconductors
UM11029
Chapter 11: LPC84x I/O configuration (IOCON)
MODE bit is controlled by FAIM value during reset, two FAIM bits data for each PAD
MODE bit. After reset release, PAD pull-up/pull-down can be updated by software. See
Section 4.2.1 “FAIM bit definitions”
.
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. 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.
11.4.4 Open-drain mode
An open-drain mode can be enabled for all digital I/O pins that are not the I2C-bus pins.
This mode is not a true open-drain mode. The input cannot be pulled up above V
DD
.
Remark:
As opposed to the true open-drain I2C-bus pins, digital pins with configurable
open-drain mode are
not
5 V tolerant when V
DD
= 0.
11.4.5 Analog mode
The switch matrix automatically configures the pin in analog mode whenever an analog
input or output is selected as the pin’s function. In analog mode, the internal pull-up
should be disabled via IOCON register.
11.4.6 I
2
C-bus mode
The I
2
C-bus pins PIO0_10 and PIO0_11 can be programmed to support a true open-drain
mode independently of whether the I2C function is selected or another digital function. If
the I
2
C function is selected, all three I
2
C modes, Standard mode, Fast-mode, and
Fast-mode plus, are supported. A digital glitch filter can be configured for all functions.
Pins PIO0_10 and PIO0_11 operate as high-current sink drivers (20 mA) independently of
the programmed function.
Remark:
Pins PIO0_10 and PIO0_11 are 5 V tolerant when V
DD
= 0 and when V
DD
is at
operating voltage level.
11.4.7 Programmable digital filter
All GPIO pins are equipped with a programmable, digital glitch filter. The filter rejects input
pulses with a selectable duration of shorter than one, two, or three cycles of a filter clock
(S_MODE = 1, 2, or 3). For each individual pin, the filter clock can be selected from one of
seven peripheral clocks PCLK0 to 6, which are derived from the main clock using the
IOCONCLKDIV0 to 6 registers. The filter can also be bypassed entirely.
Any input pulses of duration T
pulse
of either polarity will be rejected if:
T
pulse
T
PCLKn
S_MODE
Input pulses of one filter clock cycle longer may also be rejected:
T
pulse
T
PCLKn
´ ( 1)