RX610 Group
10. ICU
R01UH0032EJ0120 Rev.1.20
Page 250 of 1006
Feb 20, 2013
10.5
Non-maskable Interrupt Operation
The interrupt on the non-maskable interrupt (NMI) pin serves as an NMI. Specifically, a rising or falling edge of the
signal on the NMI pin issues an NMI request for the CPU. The DTC and DMAC are not selectable as destinations for the
NMI. The NMI takes precedence over all other interrupts, including the fast interrupt.
Upon detection of an NMI, the NMI status flag (NMIST bit) in NMISR is set to 1, and an NMI request is issued for the
CPU. An NMI request is accepted regardless of the settings of the I bit (interrupt enable bit) and IPL[2:0] bits (processor
interrupt priority level) in the PSW of the CPU.
To clear the NMIST flag in NMISR, write 1 to the NMICLR bit in NMICLR. Then, before executing the next instruction,
confirm that the NMIST flag in NMISR has been cleared.
To prevent malfunctions in systems that do not require interrupts via the NMI pin, the NMI is disabled by default. If a
system is to use the NMI, the procedure below must be included at the beginning of processing by all programs.
Procedure for Using the NMI
1.
Set the stack pointer (SP).
2.
Make the detection setting for the NMI in the NMIMD bit.
3.
Clear the NMIST flag in NMISR by writing 1 to the NMICLR bit in NMICLR, and then confirm that the flag is
actually cleared.
4.
Write 1 to the NMIEN bit in NMIER to enable the NMI.
After the NMIEN bit in NMIER is set to 1, subsequent write access to the bit is ignored. The NMI cannot be disabled.
This feature is essential if the NMI is in use, since it prevents unintentional disabling of the NMI due to a program
crashing.
For the flow of non-maskable interrupt processing, see section 9, Exceptions.
Summary of Contents for RX600 Series
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