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M16C/29 Group
9.4.4 Returning from an Interrupt Routine
The FLG register and PC in the state in which they were immediately before entering the interrupt
sequence are restored from the stack by executing the REIT instruction at the end of the interrupt
routine. Thereafter the CPU returns to the program which was being executed before accepting the
interrupt request.
Return the other registers saved by a program within the interrupt routine using the POPM or similar
instruction before executing the REIT instruction.
9.5 Interrupt Priority
If two or more interrupt requests are generated while executing one instruction, the interrupt request that
has the highest priority is accepted.
For maskable interrupts (peripheral functions), any desired priority level can be selected using the ILVL2
to ILVL0 bits. However, if two or more maskable interrupts have the same priority level, their interrupt
priority is resolved by hardware, with the highest priority interrupt accepted.
The watchdog timer and other special interrupts have their priority levels set in hardware. Figure 9.5.1
shows the priorities of hardware interrupts.
Software interrupts are not affected by the interrupt priority. If an instruction is executed, control branches
invariably to the interrupt routine.
Figure 9.5.1. Hardware Interrupt Priority
9.5.1 Interrupt Priority Resolution Circuit
The interrupt priority resolution circuit is used to select the interrupt with the highest priority among
those requested.
Figure 9.5.1.1 shows the circuit that judges the interrupt priority level.
Rev.1.00 Nov 01,2004
REJ09B0101-0100Z
Oscillation stop and re-oscillation
voltage down detection
page 74 of 402
Reset
NMI
DBC
detection,
Peripheral function
Single step
Address match
High
Low
9. Interrupts
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