Z8F1680SH020SG Datasheet, PDF (165/412 Pages) Zilog, Inc. – High-Performance 8-Bit Microcontrollers

Z8 Encore! XP^® F1680 Series
Product Specification
140
Chapter 11. Watchdog Timer
The Watchdog Timer (WDT) function helps protect against corrupted or unreliable soft-
ware and other system-level problems that can place the Z8 Encore! XP F1680 Series
MCU into unsuitable operating states. The WDT includes the following features:
• On-chip RC oscillator
• A selectable time-out response: Reset or System Exception
• 16-bit programmable time-out value
11.1. Operation
The WDT is a retriggerable one-shot timer that resets or interrupts the Z8 Encore! XP
F1680 Series when the WDT reaches its terminal count. The WDT uses its own dedicated
on-chip RC oscillator as its clock source. The WDT has only two modes of operation—
ON and OFF. After it is enabled, the WDT always counts and must be refreshed to prevent
a time-out. An enable can be performed by executing the WDT instruction or by writing
the WDT_AO option bit. When cleared to 0, the WDT_AO bit enables the WDT to
operate continuously, 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 WDTEN bit in the Oscillator Control 0 Register (OSCCTL0)¹. If
the RC oscillator is disabled, the WDT will not operate.
The WDT 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
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 computed using {WDTH[7:0],
WDTL[7:0]} and the typical Watchdog Timer RC Oscillator frequency is 10 kHz. Users
must consider system requirements when selecting the time-out delay. Table 80 indicates
the approximate time-out delays for the default and maximum WDT reload values.
1. For details about this register, see Table 170 on page 319.
PS025015-1212
PRELIMINARY
Watchdog Timer