R8C/13 Group
10.1 Interrupt Overview
• 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.
• 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 10.8
shows the Hardware Interrupt Priority.
Software interrupts are not affected by the interrupt priority. If an instruction is executed, control
branches invariably to the interrupt routine.
Reset > WDT/Oscillation stop detection/Voltage detection > Peripheral function > Single step > Address match
Figure 10.8 Hardware Interrupt Priority
Rev.1.20 Jan 27, 2006 page 58 of 205
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