w78l812a Winbond Electronics Corp America, w78l812a Datasheet - Page 12

• Manufacturer Part Number: w78l812a
• Description: 8-bit Mcu Series 80c51-based
• Manufacturer: Winbond Electronics Corp America

5.6
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.
5.6.1
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.
Watchdog Timer
Watchdog Timer Control Register
under IDLE mode. Default is cleared.
Bit:
0
0
0
0
1
1
1
1
PS2 PS1 PS0
ENW
0
1
0
1
0
0
1
1
7
0
0
1
1
0
1
0
1
CLRW
OSC
Mnemonic: WDTC
6
1
×
2
14
WIDL
5
×
PRESCALER
- 12 -
4
-
×
Address: 8FH
1000 12
3
-
W78LE812/W78L812A
PRESCALER SELECT
×
PS2
mS
2
128
256
16
32
64
2
4
8
PS1
1
PS0
0