M16C6K9 Datasheet, PDF (54/292 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6K9 Group
Interrupt
Returning from an Interrupt Routine
Executing the REIT instruction at the end of an interrupt routine returns the contents of the flag register (FLG)
as it was immediately before the start of interrupt sequence and the contents of the program counter (PC),
both of which have been saved in the stack area. Then control returns to the program that was being
executed before the acceptance of the interrupt request, so that the suspended process resumes.
Return the other registers saved by software within the interrupt routine using the POPM or similar instruc-
tion before executing the REIT instruction.
Interrupt Priority
If there are two or more interrupt requests occurring at a point in time within a single sampling (checking
whether interrupt requests are made), the interrupt assigned a higher priority is accepted.
Assign an arbitrary priority to maskable interrupts (peripheral I/O interrupts) using the interrupt priority level
select bits. If the same interrupt priority level is assigned, however, the interrupt with higher hardware priority
is accepted.
Priorities of the special interrupts, such as Reset (dealt with as an interrupt assigned the highest priority),
watchdog timer interrupt, etc. are regulated by hardware.
Fig.DD-9 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
Interrupt priority level judgement circuit
When two or more interrupts are generated simultaneously, this circuit selects the interrupt with the highest
priority level. Fig.DD-10 shows the circuit that judges the interrupt priority level..
Rev.1.00 Jun 06, 2003 page 54 of 290