z8f0822 ZiLOG Semiconductor, z8f0822 Datasheet - Page 96

• Manufacturer Part Number: z8f0822
• Description: High Performance 8-bit Microcontrollers
• Manufacturer: ZiLOG Semiconductor

Watchdog Timer
Operation
PS022517-0508
Watchdog Timer (WDT) protects against corrupt or unreliable software, power faults, and
other system-level problems which can place the Z8 Encore! XP
into unsuitable operating states. It includes the following features:
•
•
•
WDT is a retriggerable one-shot timer that resets or interrupts the Z8 Encore! XP F0822
Series device when the WDT reaches its terminal count. It uses its own dedicated on-chip
RC oscillator as its clock source. The WDT has only two modes of operation—ON and
OFF. When enabled, it always counts and must be refreshed to prevent a time-out. An
enable is performed by executing the WDT instruction or by setting the
Bit. The
has not been executed.
The WDT 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 Watchdog Timer RC oscillator
frequency is 10 kHz. WDT cannot be refreshed once it reaches
Reload Value must not be set to values below
approximate time-out delays for minimum and maximum WDT reload values.
Table 47. Watchdog Timer Approximate Time-Out Delays
WDT Time-out Period (ms)
WDT Reload
Value
(Hex)
000004
FFFFFF
On-chip RC oscillator.
A selectable time-out response—Reset or Interrupt.
24-bit programmable time-out value.
WDT_AO
WDT Reload
Value
bit enables the WDT to operate all the time, even if a WDT instruction
16,777,215
(Decimal)
4
=
WDT Reload Value
-------------------------------------------------- -
Approximate Time-Out Delay
(with 10 kHz typical WDT Oscillator Frequency)
10
1677.5 s
Typical
400 μs
000004H
.
Z8 Encore! XP
Table 47
000002H
Product Specification
®
Description
Minimum time-out delay
Maximum time-out delay
provides information on
F0822 Series device
WDT_AO
®
. The WDT
F0822 Series
Watchdog Timer
Option
83