
UM10800
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© NXP Semiconductors N.V. 2016. All rights reserved.
User manual
Rev. 1.2 — 5 October 2016
91 of 487
NXP Semiconductors
UM10800
Chapter 8: LPC82x I/O configuration (IOCON)
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.
8.4.4 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.
8.4.5 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.
8.4.6 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.
8.4.7 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)
Remark:
The filtering effect is accomplished by requiring that the input signal be stable for
(1) successive edges of the filter clock before being passed on to the chip.
Enabling the filter results in delaying the signal to the internal logic and should be done
only if specifically required by an application. For high-speed or time critical functions
ensure that the filter is bypassed.
If the delay of the input signal must be minimized, select a faster PCLK and a higher
sample mode (S_MODE) to minimize the effect of the potential extra clock cycle.