W77IE58 Datasheet, PDF (67/90 Pages) Winbond – 8-BIT MICROCONTROLLER

Preliminary W77IE58
Table 9. Time-out values for the Watchdog timer
WD1
0
0
1
1
WD0
0
1
0
1
Watchdog
Interval
17
2
20
2
23
2
26
2
Number of
Clocks
131072
1048576
8388608
67108864
Time
@ 1.8432 MHz
71.11 mS
568.89 mS
4551.11 mS
36408.88 mS
Time
@ 10 MHz
13.11 mS
104.86 mS
838.86 mS
6710.89 mS
Time
@ 25 MHz
5.24 mS
41.94 mS
335.54 mS
2684.35 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.
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 EWT = 0, then this bit will not be affected by
the watchdog timer.
EWT:
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.
RWT:
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 RWT 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.
Clock Control
WD1, WD0: CKCON.7, CKCON.6 - Watchdog Timer Mode select bits. These two bits select the time-
out interval for the watchdog timer. The reset time is 512 clock longer than the interrupt
time-out value.
The default Watchdog time-out is 2¹⁷ clocks, which is the shortest time-out period. The EWT, WDIF and
RWT bits are protected by the Timed Access procedure. This prevents software from accidentally
enabling or disabling the watchdog timer. More importantly, it makes it highly improbable that errant
code can enable or disable the watchdog timer.
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Publication Release Date: July 2000
Revision A1