Z8FMC16100 Series Flash MCU
Product Specification
63
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_AOOption Bit. The WDT_AObit 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 WDTENbit 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:
WDT Reload Value
WDT Time-Out Period (ms) =
10
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.
PS024604-1005
P R E L I M I N A R Y
Operation
ZILOG [ ZILOG, INC. ]
