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Section 4 Exception Handling
4.1
Exception Handling Types and Priority
As table 4.1 indicates, exception handling may be caused by a reset, trace, interrupt, or trap
instruction. Exception handling is prioritized as shown in table 4.1. If two or more exceptions
occur simultaneously, they are accepted and processed in order of priority. Exception sources, the
stack structure, and operation of the CPU vary depending on the interrupt control mode. For
details on the interrupt control mode, refer to section 5, Interrupt Controller.
Table 4.1
Exception Types and Priority
Priority Exception Type
Start of Exception Handling
High
Reset
Starts immediately after a low-to-high transition at the
RES
pin, or when the watchdog timer overflows. The CPU enters
the reset state when the
RES
pin is low
Trace
*
1
Starts when execution of the current instruction or exception
handling ends, if the trace (T) bit in the EXR is set to 1.
Direct
transition
*
2
Starts when the direct transition occurs by execution of the
SLEEP instruction.
Interrupt
Starts when execution of the current instruction or exception
handling ends, if an interrupt request has been issued.
Interrupt detection is not performed on completion of ANDC,
ORC, XORC, or LDC instruction execution, or on completion
of reset exception handling.
Low
Trap instruction
Started by execution of a trap instruction (TRAPA)
Trap instruction exception handling requests are accepted at
all times in program execution state.
Notes: 1. Traces are enabled only in interrupt control mode 2. Trace exception handling is not
executed after execution of an RTE instruction.
2. Not available in this LSI.
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