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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
21 of 808
NXP Semiconductors
UM10360
Chapter 3: LPC17xx System control
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
3–6.3 “External Interrupt Mode register (EXTMODE - 0x400F C148)”
and
“External Interrupt Polarity register (EXTPOLAR - 0x400F C14C)”
For example, if a system wakes up from Power-down using low level on external interrupt
0 pin, its post wake-up code must reset EINT0 bit in order to allow future entry into the
Power-down mode. If 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.
[1]
Example:
e.g. if the EINTx is selected to be low level sensitive and low level is present on
corresponding pin, this bit can not be cleared; this bit can be cleared only when signal on the
pin becomes high.
6.3 External Interrupt Mode register (EXTMODE - 0x400F 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
) and enabled in the appropriate
NVIC register) can cause interrupts from the External Interrupt function (though of course
pins selected for other functions may cause interrupts from those functions).
Table 10.
External Interrupt Flag register (EXTINT - address 0x400F C140) bit description
Bit
Symbol Description
Reset
value
0
EINT0
In level-sensitive mode, this bit is set if the EINT0 function is selected for its
pin, and the pin is in its active state. In edge-sensitive mode, this bit is set if
the EINT0 function is selected for its pin, and the selected edge occurs on
the pin.
This bit is cleared by writing a one to it, except in level sensitive mode when
the pin is in its active state.
0
1
EINT1
In level-sensitive mode, this bit is set if the EINT1 function is selected for its
pin, and the pin is in its active state. In edge-sensitive mode, this bit is set if
the EINT1 function is selected for its pin, and the selected edge occurs on
the pin.
This bit is cleared by writing a one to it, except in level sensitive mode when
the pin is in its active state.
0
2
EINT2
In level-sensitive mode, this bit is set if the EINT2 function is selected for its
pin, and the pin is in its active state. In edge-sensitive mode, this bit is set if
the EINT2 function is selected for its pin, and the selected edge occurs on
the pin.
This bit is cleared by writing a one to it, except in level sensitive mode when
the pin is in its active state.
0
3
EINT3
In level-sensitive mode, this bit is set if the EINT3 function is selected for its
pin, and the pin is in its active state. In edge-sensitive mode, this bit is set if
the EINT3 function is selected for its pin, and the selected edge occurs on
the pin.
This bit is cleared by writing a one to it, except in level sensitive mode when
the pin is in its active state.
0
7:4
-
Reserved, user software should not write ones to reserved bits. The value
read from a reserved bit is not defined.
NA