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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
87 of 368
NXP Semiconductors
UM10375
Chapter 7: LPC13xx I/O configuration
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
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.
7.3.3 Hysteresis
The input buffer for digital functions can be configured with hysteresis or as plain buffer
through the IOCON registers (see the
LPC1311/13/43/44 data sheet
for details).
If the external pad supply voltage V
DD
is between 2.5 V and 3.6 V, the hysteresis buffer
can be enabled or disabled. If V
DD
is below 2.5 V, the hysteresis buffer must be
disabled
to use the pin in input mode.
7.3.4 A/D-mode
In A/D-mode, the digital receiver is disconnected to obtain an accurate input voltage for
analog-to-digital conversions. This mode is available in those IOCON registers that
control pins which can function as ADC inputs. If A/D mode is selected, Hysteresis and
Pin mode settings have no effect.
7.3.5 Open-drain Mode
When output is selected, either by selecting a special function in the FUNC field, or by
selecting GPIO function for a pin having a 1 in its GPIODIR register, a 1 in the OD bit
selects open-drain operation, that is, a 1 disables the high-drive transistor. This option has
no effect on the primary I
2
C pins.
Remark:
The open-drain mode is only available on parts LPC1311/01 and LPC1313/01.
7.3.6 I
2
C mode
If the I
2
C function is selected by the FUNC bits of registers IOCON_PIO0_4 (
)
and IOCON_PIO0_5 (
), then the I
2
C-bus pins can be configured for different
I
2
C-modes:
•
Standard mode/Fast-mode I
2
C with input glitch filter (this includes an open-drain
output according to the I
2
C-bus specification).
•
Fast-mode Plus with input glitch filter (this includes an open-drain output according to
the I
2
C-bus specification). In this mode, the pins function as high-current sinks.
•
Standard, open-drain I/O functionality without input filter.
Remark:
Either Standard mode/Fast-mode I
2
C or Standard I/O functionality should be
selected if the pin is used as GPIO pin.
7.4 Register description
The I/O configuration registers control the following pins: PIO ports, the I
2
C-bus pins, and
the ADC input pins.