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10.1 Overview
The H8/3039 Series has an on-chip watchdog timer (WDT). The WDT has two selectable
functions: it can operate as a watchdog timer to supervise system operation, or it can operate as an
interval timer. As a watchdog timer, it generates a reset signal for the H8/3039 Series chip if a
system crash allows the timer counter (TCNT) to overflow before being rewritten. In interval
timer operation, an interval timer interrupt is requested at each TCNT overflow.
10.1.1 Features
WDT features are listed below.
• Selection of eight counter clock sources
• ø/2, ø/32, ø/64, ø/128, ø/256, ø/512, ø/2048, or ø/4096
• Interval timer option
• Timer counter overflow generates a reset signal or interrupt.
• The reset signal is generated in watchdog timer operation. An interval timer interrupt is
generated in interval timer operation.
• Watchdog timer reset signal resets the entire H8/3039 Series chip internally, and can also be
output externally.*
The reset signal generated by timer counter overflow during watchdog timer operation resets the
entire H8/3039 Series internally. An external reset signal can be output from the RESO pin to reset
other system devices simultaneously.
Note: * The RESO pin of the masked ROM version is the dedicated FWE input pin of the F-ZTAT
version. Therefore, the F-ZTAT version cannot output the reset signal to the outside.
Section 10 Watchdog Timer
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