M16C1N Datasheet, PDF (70/238 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/10 SERIES

M16C/1N Group
10. Interrupt
10.1.5.9 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 sus-
pended process resumes.
Return the other registers saved by software within the interrupt routine using the POPM or similar
instruction before executing the REIT instruction.
10.1.5.10 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 ac-
cepted.
Assign an arbitrary priority to maskable interrupts (peripheral I/O interrupts) using the interrupt
priority level select bit. If the same interrupt priority level is assigned, however, the interrupt as-
signed a 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.
Figure 10.8 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.
Reset
High
UART0 reception
DBC
Watchdog timer/Oscillation stop detection
Peripheral function
Single step
Address match
Low
Figure 10.8 Hardware interrupts priorities
10.1.5.11 Interrupt Priority Level Judge Circuit
This circuit selects the interrupt with the highest priority level when two or more interrupts are
generated simultaneously.
Figure 10.9 shows the interrupt resolution circuit.
Rev.1.00 Oct 20, 2004 page 58 of 222
REJ09B0007-0100Z