Z8 Encore! XP® 4K Series
Product Specification
83
Watch-Dog Timer
Overview
The Watch-Dog Timer (WDT) protects against corrupt or unreliable software, power
faults, and other system-level problems which may place the Z8 Encore! XP® 4K Series
devices into unsuitable operating states. The Watch-Dog Timer includes the following fea-
tures:
•
•
•
On-chip RC oscillator
A selectable time-out response: reset or interrupt
24-bit programmable time-out value
Operation
The Watch-Dog Timer (WDT) is a one-shot timer that resets or interrupts the Z8 Encore!
XP® 4K Series devices when the WDT reaches its terminal count. The Watch-Dog Timer
uses a dedicated on-chip RC oscillator as its clock source. The Watch-Dog Timer operates
in only 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 Watch-Dog Timer to operate
immediately upon reset, 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
described by the following equation:
WDT Reload Value
WDT Time-out Period (ms) = -------------------------------------------------
10
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 10KHz. The Watch-Dog Timer cannot be refreshed after it reaches 000002H.
The WDT Reload Value must not be set to values below 000004H. Table 57 provides
information about approximate time-out delays for the minimum and maximum WDT
reload values.
PS022815-0206
Watch-Dog Timer
ZILOG [ ZILOG, INC. ]
