Overview of Interrupts
7-3
Interrupts
Table 7–1. Interrupt Priorities
ÁÁÁÁÁÁÁÁ
Á
ÁÁÁÁÁÁ
Á
ÁÁÁÁÁÁÁÁ
Priority
ÁÁÁÁÁÁÁ
Á
ÁÁÁÁÁ
Á
ÁÁÁÁÁÁÁ
Interrupt
Name
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
Highest
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Reset
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
NMI
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT4
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT5
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT6
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT7
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT8
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT9
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT10
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT11
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT12
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT13
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT14
ÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁ
Lowest
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
INT15
7.1.1.1
Reset (RESET)
Reset is the highest priority interrupt and is used to halt the CPU and return
it to a known state. The reset interrupt is unique in a number of ways:
-
RESET is an active-low signal. All other interrupts are active-high signals.
-
RESET must be held low for 10 clock cycles before it goes high again to
reinitialize the CPU properly.
-
The instruction execution in progress is aborted and all registers are
returned to their default states.
-
The reset interrupt service fetch packet must be located at address 0.
-
RESET is not affected by branches.
7.1.1.2
Nonmaskable Interrupt (NMI)
NMI is the second-highest priority interrupt and is generally used to alert the
CPU of a serious hardware problem such as imminent power failure.
For NMI processing to occur, the nonmaskable interrupt enable (NMIE) bit in
the interrupt enable register must be set to 1. If NMIE is set to 1, the only condi-
tion that can prevent NMI processing is if the NMI occurs during the delay slots
of a branch (whether the branch is taken or not).
NMIE is cleared to 0 at reset to prevent interruption of the reset. It is cleared
at the occurrence of an NMI to prevent another NMI from being processed. You
cannot manually clear NMIE, but you can set NMIE to allow nested NMIs.
While NMI is cleared, all maskable interrupts (INT4–INT15) are disabled.