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M0A21/M0A23 Series
May 06, 2022
Page
158
of 746
Rev 1.02
M0
A21
/M
0
A
2
3
SE
RIES
TEC
H
NICAL
RE
FEREN
C
E
M
ANUAL
43
27
USCI1
USCI1 interrupt
44
28
PWRWU_INT
Clock controller interrupt for chip wake-up from power-down state
45
29
ADC_INT
ADC interrupt
46
30
CLKFAIL
Clock fail detected or IRC Auto Trim interrupt
47
31
Reserved
Reserved
Table 6.2-9 Interrupt Number Table
Vector Table
When an interrupt is accepted, the processor will automatically fetch the starting address of the interrupt
service routine (ISR) from a vector table in memory. For Armv6-M, the vector table base address is fixed
at 0x00000000. The vector table contains the initialization value for the stack pointer on reset, and the
entry point addresses for all exception handlers. The vector number on previous page defines the order
of entries in the vector table associated with exception handler entry as illustrated in previous section.
Vector Table Word Offset
Description
0
SP_main
– The Main stack pointer
Vector Number
Exception Entry Pointer using that Vector Number
Table 7.2-10 Vector Figure Format
Operation Description
NVIC interrupts can be enabled and disabled by writing to their corresponding Interrupt Set-Enable or
Interrupt Clear-Enable register bit-field. The registers use a write-1-to-enable and write-1-to-clear policy,
both registers reading back the current enabled state of the corresponding interrupts. When an interrupt
is disabled, interrupt assertion will cause the interrupt to become Pending, however, the interrupt will
not be activated. If an interrupt is Active when it is disabled, it remains in its Active state until cleared by
reset or an exception return. Clearing the enable bit prevents new activations of the associated interrupt.
NVIC interrupts can be pended/un-pended using a complementary pair of registers to those used to
enable/disable the interrupts, named the Set-Pending Register and Clear-Pending Register
respectively. The registers use a write-1-to-enable and write-1-to-clear policy, both registers reading
back the current pended state of the corresponding interrupts. The Clear-Pending Register has no effect
on the execution status of an Active interrupt.
NVIC interrupts are prioritized by updating an 8-bit field within a 32-bit register (each register supporting
four interrupts).
The general registers associated with the NVIC are all accessible from a block of memory in the System
Control Space and will be described in next section.