Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 106 of 547
NXP Semiconductors
UM10398
Chapter 8: LPC1100XL series: I/O configuration (IOCONFIG)
8.3.1 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 Section 12.3.2
). 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.
8.3.2 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. If the pull-up resistor is enabled
(default), all non-I2C pins are pulled up to 3.3 V (V
DD
= 3.3 V).
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. The state retention is
Fig 15. Standard I/O pin configuration
PIN
V
DD
V
DD
ESD
V
SS
ESD
strong
pull-up
strong
pull-down
V
DD
weak
pull-up
weak
pull-down
open-drain enable
output enable
repeater mode
enable
pull-up enable
pull-down enable
data output
data input
analog input
select analog input
002aah159
pin configured
as digital output
driver
pin configured
as digital input
pin configured
as analog input