UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 31 of 792
NXP Semiconductors UM10237
Chapter 3: LPC24XX System control
3.1.3 External Interrupt Mode register (EXTMODE - 0xE01F C148)
The bits in this register select whether each EINT pin is level- or edge-sensitive. Only pins
that are selected for the EINT function (see Section 9–5.5) and enabled in the
VICIntEnable register (Section 7–3.4 “Interrupt Enable Register (VICIntEnable -
0xFFFF F010)) can cause interrupts from the External Interrupt function (though of
course pins selected for other functions may cause interrupts from those functions).
Note: Software should only change a bit in this register when its interrupt is
disabled in VICIntEnable, and should write the corresponding 1 to EXTINT before
enabling (initializing) or re-enabling the interrupt. An extraneous interrupt(s) could
be set by changing the mode and not having the EXTINT cleared.
3.1.4 External Interrupt Polarity register (EXTPOLAR - 0xE01F C14C)
In level-sensitive mode, the bits in this register select whether the corresponding pin is
high- or low-active. In edge-sensitive mode, they select whether the pin is rising- or
falling-edge sensitive. Only pins that are selected for the EINT function (see
Section 9–5.5) and enabled in the VICIntEnable register (Section 7–3.4 “Interrupt Enable
Register (VICIntEnable - 0xFFFF F010)) can cause interrupts from the External Interrupt
function (though of course pins selected for other functions may cause interrupts from
those functions).
Note: Software should only change a bit in this register when its interrupt is
disabled in VICIntEnable, and should write the corresponding 1 to EXTINT before
enabling (initializing) or re-enabling the interrupt. An extraneous interrupt(s) could
be set by changing the polarity and not having the EXTINT cleared.
Table 26. External Interrupt Mode register (EXTMODE - address 0xE01F C148) bit
description
Bit Symbol Value Description Reset
value
0 EXTMODE0 0 Level-sensitivity is selected for EINT0.0
1EINT0
is edge sensitive.
1 EXTMODE1 0 Level-sensitivity is selected for EINT1.0
1EINT1
is edge sensitive.
2 EXTMODE2 0 Level-sensitivity is selected for EINT2.0
1EINT2
is edge sensitive.
3 EXTMODE3 0 Level-sensitivity is selected for EINT3.0
1EINT3
is edge sensitive.
7:4 - - Reserved, user software should not write ones to reserved
bits. The value read from a reserved bit is not defined. NA