z8f1601 ZiLOG Semiconductor, z8f1601 Datasheet - Page 90

• Manufacturer Part Number: z8f1601
• Description: Z8 Encore!? Microcontroller With Flash Memory And 10-bit A/d Converter
• Manufacturer: ZiLOG Semiconductor

Watch-Dog Timer
Overview
Operation
PS017609-0803
The Watch-Dog Timer (WDT) helps protect against corrupt or unreliable software, power
faults, and other system-level problems which may place the Z8 Encore!
operating states. The Watch-Dog Timer includes the following features:
•
•
•
The Watch-Dog Timer (WDT) is a retriggerable one-shot timer that resets or interrupts the
Z8F640x family device 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.
The Watch-Dog Timer is a 24-bit reloadable downcounter that uses three 8-bit registers in
the eZ8 CPU register space to set the reload value. The nominal WDT time-out period is
given by the following equation:
where the WDT reload value is the decimal value of the 24-bit value given by
{WDTU[7:0], WDTH[7:0], WDTL[7:0]} and the typical Watch-Dog Timer RC oscillator
frequency is 50kHz. The Watch-Dog Timer cannot be refreshed once it reaches
The WDT Reload Value must not be set to values below
WDT Time-out Period (ms)
On-chip RC oscillator
A selectable time-out response: Short Reset or interrupt
24-bit programmable time-out value
=
WDT Reload Value
------------------------------------------------- -
50
000004H
. Table 45 provides
Watch-Dog Timer
®
into unsuitable
Z8 Encore!
000002H
®
.
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