HD64F2149YV datasheet(437/1075 Pages) RENESAS

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Section 14 Watchdog Timer (WDT)

Rev. 3.00 Jan 18, 2006 page 409 of 1044

REJ09B0280-0300

Section 14 Watchdog Timer (WDT)

14.1

Overview

The H8S/2169 or H8S/2149 has an on-chip watchdog timer with two channels (WDT0, WDT1)

for monitoring system operation. The WDT outputs an overflow signal (

RESO) if a system crash

prevents the CPU from writing to the timer counter, allowing it to overflow. At the same time, the

WDT can also generate an internal reset signal or internal NMI interrupt signal.

When this watchdog function is not needed, the WDT can be used as an interval timer. In interval

timer mode, an interval timer interrupt is generated each time the counter overflows.

14.1.1

Features

WDT features are listed below.

• Switchable between watchdog timer mode and interval timer mode

• Internal reset or internal interrupt generated when the timer counter overflows

 WOVI interrupt generation in interval timer mode

 Choice of internal reset or NMI interrupt generation in watchdog timer mode

• RESO output in watchdog timer mode

 In watchdog timer mode, a low-level signal is output from the RESO pin when the counter

overflows (when internal reset is selected)

• Choice of 8 (WDT0) or 16 (WDT1) counter input clocks

 Maximum WDT interval: system clock period × 131072 × 256

 Subclock can be selected for the WDT1 input counter

Maximum interval when the subclock is selected: subclock period

× 256 × 256

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