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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
20 of 808
NXP Semiconductors
UM10360
Chapter 3: LPC17xx System control
But when Brown-Out Detection is enabled to bring the LPC17xx out of Power-down mode
(which is itself not a guaranteed operation -- see
Section 4–8.7 “Power Mode Control
register (PCON - 0x400F C0C0)”
), the supply voltage may recover from a transient before
the wake-up timer has completed its delay. In this case, the net result of the transient BOD
is that the part wakes up and continues operation after the instructions that set
Power-down mode, without any interrupt occurring and with the BOD bit in the RSID being
0. Since all other wake-up conditions have latching flags (see
Interrupt flag register (EXTINT - 0x400F C140)”
), a wake-up of this
type, without any apparent cause, can be assumed to be a Brown-Out that has gone
away.
6.
External interrupt inputs
TheLPC17xx includes four External Interrupt Inputs as selectable pin functions. In
addition, external interrupts have the ability to wake up the CPU from Power-down mode.
Refer to
Section 4–8.8 “Wake-up from Reduced Power Modes”
for details.
6.1 Register description
The external interrupt function has four registers associated with it. The EXTINT register
contains the interrupt flags. The EXTMODE and EXTPOLAR registers specify the level
and edge sensitivity parameters.
[1]
Reset Value reflects the data stored in used bits only. It does not include reserved bits content.
6.2 External Interrupt flag register (EXTINT - 0x400F C140)
When a pin is selected for its external interrupt function, the level or edge on that pin
(selected by its bits in the EXTPOLAR and EXTMODE registers) will set its interrupt flag in
this register. This asserts the corresponding interrupt request to the NVIC, which will
cause an interrupt if interrupts from the pin are enabled.
Writing ones to bits EINT0 through EINT3 in EXTINT register clears the corresponding
bits. In level-sensitive mode the interrupt is cleared only when the pin is in its inactive
state.
Once a bit from EINT0 to EINT3 is set and an appropriate code starts to execute (handling
wake-up and/or external interrupt), this bit in EXTINT register must be cleared. Otherwise
event that was just triggered by activity on the EINT pin will not be recognized in future.
Table 9.
External Interrupt registers
Name
Description
Access Reset
value
Address
EXTINT
The External Interrupt Flag Register contains
interrupt flags for EINT0, EINT1, EINT2 and
EINT3. See
.
R/W
0x00
0x400F C140
EXTMODE
The External Interrupt Mode Register controls
whether each pin is edge- or level-sensitive.
See
R/W
0x00
0x400F C148
EXTPOLAR
The External Interrupt Polarity Register controls
which level or edge on each pin will cause an
interrupt. See
R/W
0x00
0x400F C14C