W79E825A Datasheet, PDF (78/127 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E825A/824A/823B/822B Data Sheet
any errant code is executed now, then the reset Watchdog Timer instructions will not be executed at
the required instants and Watchdog reset will occur.
The Watchdog Timer time-out selection will result in different time-out values depending on the clock
speed. The reset, when enabled, will occur when 512 clocks after time-out has occurred.
WD1
0
0
1
1
WD0
0
1
0
1
INTERRUPT
TIME-OUT
2¹⁷
2²⁰
2²³
2²⁶
RESET
TIME-OUT
2¹⁷ + 512
2²⁰ + 512
2²³ + 512
2²⁶ + 512
Table 15-2: Time-out values for the Watchdog Timer
NUMBER OF
CLOCKS
131072
1048576
8388608
67108864
TIME
@ 10 MHZ
13.11 mS
104.86 mS
838.86 mS
6710.89 mS
The Watchdog Timer will de disabled by a power-on/fail reset. The Watchdog Timer reset does not
disable the Watchdog Timer, but will restart it. In general, software should restart the timer to put it into
a known state. The control bits that support the Watchdog Timer are discussed below.
15.1 WATCHDOG CONTROL
WDIF: WDCON.3 - Watchdog Timer Interrupt flag. This bit is set whenever the time-out occurs in the
Watchdog Timer. If the Watchdog interrupt is enabled (EIE.4), then an interrupt will occur (if the global
interrupt enable is set and other interrupt requirements are met). Software or any reset can clear this
bit.
WTRF: WDCON.2 - Watchdog Timer Reset flag. This bit is set whenever a watchdog reset occurs.
This bit is useful for determined the cause of a reset. Software must read it, and clear it manually. A
Power-fail reset will clear this bit. If EWRST = 0, then this bit will not be affected by the Watchdog
Timer.
EWRST: WDCON.1 - Enable Watchdog Timer Reset. This bit when set to 1 will enable the Watchdog
Timer reset function. Setting this bit to 0 will disable the Watchdog Timer reset function, but will leave
the timer running.
WDCLR: WDCON.0 - Reset Watchdog Timer. This bit is used to clear the Watchdog Timer and to
restart it. This bit is self-clearing, so after the software writes 1 to it the hardware will automatically
clear it. If the Watchdog Timer reset is enabled, then the WDCLR has to be set by the user within 512
clocks of the time-out. If this is not done then a Watchdog Timer reset will occur.
- 78 -