Datasheet

ADuC836
–62–
ADuC836
–63–
Interrupt Priority
The Interrupt Enable registers are written by the user to enable
individual interrupt sources, while the Interrupt Priority registers
allow the user to select one of two priority levels for each inter-
rupt. An interrupt of a high priority may interrupt the service
routine of a low priority interrupt, and if two interrupts of differ-
ent priority occur at the same time, the higher level interrupt will
be serviced rst. An interrupt cannot be interrupted by another
interrupt of the same priority level. If two interrupts of the same
priority level occur simultaneously, a polling sequence is used to
determine which interrupt is serviced rst. The polling sequence
is shown in Table XXXVIII.
Table XXXVIII. Priority within an Interrupt Level
Source Priority Description
PSMI 1 (Highest) Power Supply Monitor Interrupt
WDS 2 Watchdog Interrupt
IE0 3 External Interrupt 0
RDY0/RDY1 4 ADC Interrupt
TF0 5 Timer/Counter 0 Interrupt
IE1 6 External Interrupt 1
TF1 7 Timer/Counter 1 Interrupt
ISPI/I2CI 8 SPI Interrupt
RI + TI 9 Serial Interrupt
TF2 + EXF2 10 Timer/Counter 2 Interrupt
TII 11 (Lowest) Time Interval Counter Interrupt
Interrupt Vectors
When an interrupt occurs, the program counter is pushed onto
the stack and the corresponding interrupt vector address is loaded
into the program counter. The interrupt vector addresses are
shown in Table XXXIX.
Table XXXIX. Interrupt Vector Addresses
Source Vector Address
IE0 0003H
TF0 000BH
IE1 0013H
TF1 001BH
RI + TI 0023H
TF2 + EXF2 002BH
RDY0/RDY1 (ADC) 0033H
ISPI/I2CI 003BH
PSMI 0043H
TII 0053H
WDS (WDIR = 1)* 005BH
*The watchdog can be congured to generate an interrupt instead of
a reset when it times out. This is used for logging errors or examining
the internal status of the microcontroller core to understand, from
a software debug point of view, why a watchdog timeout occurred.
The watchdog interrupt is slightly different from the normal inter-
rupts in that its priority level is always set to 1 and it is not possible
to disable the interrupt via the global disable bit (EA) in the IE SFR.
This is done to ensure that the interrupt will always be responded
to if a watchdog timeout occurs. The watchdog will only produce an
interrupt if the watchdog timeout is greater than zero.
REV. A
REV. A