UM10429
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User manual
Rev. 1 — 20 October 2010
51 of 258
NXP Semiconductors
UM10429
Chapter 7: LPC1102 I/O Configuration
7.3.1 Pin function
The FUNC bits in the IOCON registers can be set to GPIO (FUNC = 000) or to a
peripheral function. If the pins are GPIO pins, the GPIOnDIR registers determine whether
the pin is configured as an input or output (see
). For any peripheral function,
the pin direction is controlled automatically depending on the pin’s functionality. The
GPIOnDIR registers have no effect for peripheral functions.
7.3.2 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 at a logic HIGH and enables
the pull-down resistor if the pin is at a logic 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.
Fig 6.
Standard I/O pin configuration
PIN
V
DD
ESD
V
SS
ESD
V
DD
weak
pull-up
weak
pull-down
output enable
repeater mode
enable
output
pull-up enable
pull-down enable
data input
analog input
select analog input
002aaf304
pin configured
as digital output
driver
pin configured
as digital input
pin configured
as analog input