ZUSBOPTSC01ZAC datasheet(85/402 Pages) ZILOG

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PS024604-1005

P R E L I M I N A R Y

Operation

Z8FMC16100 Series Flash MCU

Product Specification

Watch-Dog Timer

The Watch-Dog Timer (WDT) helps protect against corrupted or unreliable software and

other system-level problems which may place the Z8FMC16100 Series Flash MCU into

unsuitable operating states. The Watch-Dog Timer includes the following features:

• On-chip RC oscillator

• A selectable time-out response: Reset or System Exception

• 16-bit programmable time-out value

Operation

The Watch-Dog Timer (WDT) is a retriggerable one-shot timer that resets or interrupts the

Z8FMC16100 Series Flash MCU when the WDT reaches its terminal count. The Watch-

Dog Timer uses its own dedicated on-chip RC oscillator as its clock source. The Watch-

Dog Timer has only two modes of operation—on and off. Once enabled, it always counts

and must be refreshed to prevent a time-out. An enable can be performed by executing the

WDT instruction or by setting the WDT_AO Option Bit. The WDT_AO bit enables the Watch-

Dog Timer to operate all the time, even if a WDT instruction has not been executed.

To minimize power consumption, the RC oscillator can be disabled. The RC oscillator is

disabled by clearing the WDTEN bit in the Oscillator Control Register. If the RC oscillator

is disabled, the WDT will not operate.

The Watch-Dog Timer is a 16-bit reloadable downcounter that uses two 8-bit registers in

the eZ8 CPU register space to set the reload value. The nominal WDT time-out period is

calculated by the following equation:

where the WDT reload value is assigned by {WDTH[7:0], WDTL[7:0]} and the typical

Watch-Dog Timer RC oscillator frequency is 10KHz. The user should consider system

requirements when selecting the time out delay. Table 39 provides information on approx-

imate time-out delays for the default and maximum WDT reload values.

WDT Time-Out Period (ms) =

WDT Reload Value

ZUSBOPTSC01ZAC Datasheet(PDF) 85 Page - Zilog, Inc.