In below article we are going to introduce watchdog timer which play an important role in the process of Winbond Microcontroller W78E0516 Embedded Binary Recovering:
As we all know that the Watchdog timer is a free-running timer which can be programmed by the user to serve as a system monitor, a time-base generator or an event timer. It is basically a set of dividers that divide the system clock. The divider output is selectable and determines the time-out interval.
When the time-out occurs a system reset can also be caused if it is enabled. The main use of the Watchdog timer is as a system monitor. This is important in real-time control applications. In case of power glitches or electro- magnetic interference, the processor may begin to execute errant code. If this is left unchecked the entire system may crash.
The watchdog time-out selection will result in different time-out values depending on the clock speed. The Watchdog timer will de disabled on reset. In general, software should restart the Watchdog timer to put it into a known state. The control bits that support the Watchdog timer are discussed below.
Watchdog Timer Control Register
ENW : Enable watch-dog if set.
CLRW: Clear watch-dog timer and prescaler if set. This flag will be cleared automatically
WIDL : If this bit is set, watch-dog is enabled under IDLE mode. If cleared, watch-dog is disabled under IDLE mode. Default is cleared.
PS2, PS1, PS0: Watch-dog prescaler timer select. Prescaler is selected when set PS2~0 as follows:
watchdog timer scheme
The time-out period is obtained using the following equation:
OSC
´ 214 ´PRESCALER ´ 1000 ´ 12 mS
Before Watchdog time-out occurs, the program must clear the 14-bit timer by writing 1 to WDTC.6 (CLRW). After 1 is written to this bit, the 14-bit timer, prescaler and this bit will be reset on the next instruction cycle. The Watchdog timer is cleared on reset.