H8SLASH3021 datasheet(98/712 Pages) RENESAS

98 / 712 page

4. Exception Handling

Rev.2.00 Mar. 22, 2007 Page 74 of 684

REJ09B0352-0200

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

H8/3022 Group 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 10,

Watchdog Timer.

4.2.2

Reset Sequence

The H8/3022 Group 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 using

the flash memory version, hold at "Low" level for a least 1usec. 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 H8/3022 Group 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) are read, and

program execution starts from the address indicated in the vector address.

Figure 4.2 shows the reset sequence in modes 5 and 7.

H8/3021 数据表(PDF) 98 Page - Renesas Technology Corp