Z8F4822AR020SG Datasheet, PDF (100/323 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F64xx Series
Product Specification
80
Watchdog Timer
The Watchdog Timer (WDT) helps protect against corrupt or unreliable software, power
faults and other system-level problems which can place the Z8 Encore! XP F64xx Series
MCU into unsuitable operating states. The features of the Watchdog Timer include:
• On-chip RC oscillator
• A selectable time-out response
• WDT 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! XP F64xx Series devices when the WDT reaches its terminal count. The Watch-
dog Timer uses its own dedicated on-chip RC oscillator as its clock source. The Watchdog
Timer has only two modes of operation: ON and OFF. After it is 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. This WDT_AO bit enables the
Watchdog Timer to operate continuously, even if a WDT instruction has not been exe-
cuted.
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
In the above equation, the WDT reload value is the decimal value of the 24-bit value pro-
vided by {WDTU[7:0], WDTH[7:0], WDTL[7:0]}; the typical Watchdog Timer RC oscil-
lator 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 47 lists approximate time-out delays for the minimum and maximum WDT reload
values.
PS019924-0113
PRELIMINARY
Watchdog Timer