H8SLASH3028 datasheet(102/923 Pages) RENESAS

102 / 923 page

Rev. 2.00, 09/03, page 72 of 890

4.2

Reset

4.2.1

Overview

A reset is the highest-priority exception. 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 the

on-chip supporting modules. Reset exception handling begins when the

RES pin changes from

low to high.

The chip can also be reset by overflow of the watchdog timer. For details see section 12,

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 10 system clock (φ) cycles. When the

flash memory and flash memory R versions are used, the

RES pin must be held low for at least 20

system clock cycles. See appendix D.2, Pin States at Reset, for the states of the pins in the reset

state.

When the

RES pin goes high after being held low for the necessary time, the chip starts reset

exception handling as follows.

• 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.

• The contents of the reset vector address (H'0000 to H'0003 in advanced mode, H'0000 to

H'0001 in normal mode) are read, and program execution starts from the address indicated in

the vector address.

Figure 4.2 shows the reset sequence in modes 1 and 3. Figure 4.3 shows the reset sequence in

modes 2 and 4. Figure 4.4 shows the reset sequence in mode 6.

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