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4.2
Reset
4.2.1
Overview
A reset has the highest exception priority.
When the RES pin goes low, all processing halts and the chip enters the reset state. A reset
initializes the internal state of the CPU and the registers of on-chip supporting modules.
Immediately after a reset, interrupt control mode 0 is set.
Reset exception handling begins when the RES pin changes from low to high.
A reset can also be caused by watchdog timer overflow. For details see section 11, Watchdog
Timer.
4.2.2
Reset Sequence
The chip enters the reset state when the RES pin goes low.
To ensure that the chip is reset, hold the RES pin low for at least 20 ms at power-up. To reset the
chip during operation, hold the RES pin low for at least 20 states.
When the RES pin goes high after being held low for the necessary time, the chip starts reset
exception handling as follows:
1. The internal state of the CPU and the registers of the on-chip supporting modules are
initialized, the T bit is cleared to 0 in EXR, and the I bit is set to 1 in EXR and CCR.
2. The reset exception vector address is read and transferred to the PC, and program execution
starts from the address indicated by the PC.
Figure 4-2 shows an example of the reset sequence.
Rev. 5.00, 12/03, page 102 of 1088
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