HD64F2149 Datasheet, PDF (124/1035 Pages) Renesas Technology Corp – Hitachi 16-Bit Single-Chip Microcomputer

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 MCU 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.
The MCU can also be reset by overflow of the watchdog timer. For details, see section 14,
Watchdog Timer.
4.2.2 Reset Sequence
The MCU 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 when powering on. To
reset the chip during operation, hold the RES pin low for at least 20 states. For pin states in a reset,
see Appendix D.1, Pin States at Reset.
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, and the I bit is set to 1 in 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.
Figures 4.2 and 4.3 show examples of the reset sequence.
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