© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 01 — 15 August 2005
21
Philips Semiconductors
UM10139
Volume 1
Chapter 3: System Control Block
[1]
Reset value reflects the data stored in used bits only. It does not include reserved bits content.
3.5.2 External
Interrupt
Flag register (EXTINT - 0xE01F 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 VIC, 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 this action is efficacious 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
wakeup and/or external interrupt), this bit in EXTINT register must be cleared. Otherwise
the event that was just triggered by activity on the EINT pin will not be recognized in the
future.
Important: whenever a change of external interrupt operating mode (i.e. active
level/edge) is performed (including the initialization of an external interrupt), the
corresponding bit in the EXTINT register must be cleared! For details see
3.5.4 “External Interrupt Mode register (EXTMODE - 0xE01F C148)”
“External Interrupt Polarity register (EXTPOLAR - 0xE01F C14C)”
For example, if a system wakes up from power-down using a low level on external
interrupt 0 pin, its post-wakeup code must reset the EINT0 bit in order to allow future entry
into the power-down mode. If the EINT0 bit is left set to 1, subsequent attempt(s) to invoke
power-down mode will fail. The same goes for external interrupt handling.
More details on power-down mode will be discussed in the following chapters.
INTWAKE
The Interrupt Wakeup Register contains four
enable bits that control whether each external
interrupt will cause the processor to wake up
from Power-down mode. See
R/W
0
0xE01F C144
EXTMODE
The External Interrupt Mode Register controls
whether each pin is edge- or level sensitive.
R/W
0
0xE01F C148
EXTPOLAR
The External Interrupt Polarity Register controls
which level or edge on each pin will cause an
interrupt.
R/W
0
0xE01F C14C
Table 8:
External interrupt registers
Name
Description
Access Reset
value
[1]
Address