w78e051c Winbond Electronics Corp America, w78e051c Datasheet - Page 7

• Manufacturer Part Number: w78e051c
• Description: 8-bit Microcontroller
• Manufacturer: Winbond Electronics Corp America

5.3 Watchdog Timer
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
PS2, PS1, PS0: Watch-dog prescaler timer select. Prescaler is selected when set PS2~0 as follows:
The time-out period is obtained using the following equation:
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.
OSC
1
×
under IDLE mode. Default is cleared.
2
14
×
PRESCALER 1000 12 mS
PS2 PS1 PS0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
Bit:
0
1
0
1
0
1
0
1
×
ENW
Mnemonic: WDTC
7
×
CLRW
6
WIDL
- 7 -
5
Address: 8FH
4
-
Publication Release Date: November 10, 2006
PRESCALER SELECT
W78E51C/W78E051C
3
-
128
256
16
32
64
2
4
8
PS2
2
PS1
1
Revision A4
PS0
0