Z8F0830HH020SG Datasheet, PDF (110/257 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore!^® F0830 Series
Product Specification
92
Watchdog Timer
The Watchdog Timer (WDT) protects from corrupted or unreliable software, power faults
and other system-level problems which can place the Z8 Encore! F0830 Series devices
into unsuitable operating states. The features of the Watchdog Timer include:
• On-chip RC oscillator
• A selectable time-out response: reset or interrupt
• 24-bit programmable time-out value
Operation
The Watchdog Timer is a retriggerable one-shot timer that resets or interrupts the Z8
Encore! F0830 Series devices when the WDT reaches its terminal count. The WDT uses a
dedicated on-chip RC oscillator as its clock source. The WDT operates only in two modes:
ON and OFF. Once enabled, it always counts and must be refreshed to prevent a time-out.
Perform an enable by executing the WDT instruction or by setting the WDT_AO Flash
option bit. The WDT_AO bit forces the WDT to operate immediately on reset, even if a
WDT instruction has not been executed.
The Watchdog 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
calculated using the following equation:
WDT Time-out Period (ms)
=
W------D-----T-----R----e--l--o---a---d----V-----a--l--u---e-
10
where the WDT reload value is the 24-bit decimal value provided by {WDTU[7:0],
WDTH[7:0], WDTL[7:0]} and the typical Watchdog Timer RC oscillator frequency is
10 KHz. The Watchdog Timer cannot be refreshed after it reaches 000002H. The WDT
reload value must not be set to values below 000004H. Table 58 provides information
about approximate time-out delays for the minimum and maximum WDT reload values.
Table 58. Watchdog Timer Approximate Time-Out Delays
WDT Reload Value
(Hex)
000004
000400
FFFFFF
WDT Reload Value
(Decimal)
4
1024
16,777,215
Approximate Time-Out Delay
(with 10 KHz Typical WDT Oscillator Frequency)
Typical
Description
400 µs
Minimum time-out delay
102 ms
Default time-out delay
28 minutes
Maximum time-out delay
PS025113-1212
Watchdog Timer