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3.1
Overview
Exception handling is performed in the H8/3937 Series and H8/3937R Series when a reset or
interrupt occurs. Table 3-1 shows the priorities of these two types of exception handling.
Table 3-1
Exception Handling Types and Priorities
Priority
Exception Source
High
Reset
Interrupt
Low
3.2
Reset
3.2.1
Overview
A reset is the highest-priority exception. The internal state of the CPU and the registers of the on-
chip peripheral modules are initialized.
3.2.2
Reset Sequence
As soon as the RES pin goes low, all processing is stopped and the chip enters the reset state.
To make sure the chip is reset properly, observe the following precautions.
• At power on: Hold the RES pin low until the clock pulse generator output stabilizes.
• Resetting during operation: Hold the RES pin low for at least 10 system clock cycles.
Reset exception handling takes place as follows.
• The CPU internal state and the registers of on-chip peripheral modules are initialized, with the
I bit of the condition code register (CCR) set to 1.
• The PC is loaded from the reset exception handling vector address (H'0000 to H'0001), after
which the program starts executing from the address indicated in PC.
Section 3 Exception Handling
Time of Start of Exception Handling
Exception handling starts as soon as the reset state is cleared
When an interrupt is requested, exception handling starts after
execution of the present instruction or the exception handling in
progress is completed
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