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Chapter 17
Interrupt/Exception Processing Function
User’s Manual U16702EE3V2UD00
17.3.3 Priorities of maskable interrupts
The INTC performs multiple interrupt servicing in which an interrupt is acknowledged while another
interrupt is being serviced. Multiple interrupts can be controlled by priority levels.
There are two types of priority level control: control based on the default priority levels, and control
based on the programmable priority levels that are specified by the interrupt priority level specification
bit (xxPRn) of the interrupt control register (xxICn). When two or more interrupts having the same prior-
ity level specified by the xxPRn bit are generated at the same time, interrupts are serviced in order
depending on the priority level allocated to each interrupt request type (default priority level) before-
hand. For more information, refer to
Table 17-1, “Interrupt/Exception Source List,” on page 685
.
The programmable priority control customizes interrupt requests into eight levels by setting the priority
level specification flag.
Note that when an interrupt request is acknowledged, the ID flag of PSW is automatically set to 1.
Therefore, when multiple interrupts are to be used, clear the ID flag to 0 beforehand (for example, by
placing the EI instruction in the interrupt service program) to set the interrupt enable mode.
Remarks: 1.
xx: Identification name of each peripheral unit (Refer to
Table 17-2, “Interrupt Control
Register (xxICn),” on page 702
)
2.
n: Peripheral unit number (Refer to
Table 17-2, “Interrupt Control Register (xxICn),”
on page 700
).
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