RNDr. VojtRNDr. Vojtěěchch KrmKrmííččekek
vojtec@vojtec@icsics..munimuni..czcz
Ing.Ing. ZbynZbyněěk Burek Burešš, Ph.D., Ph.D.
zbynekzbynek..buresbures@@unobunob..czcz
PIC12F629 / 675
Using Watchdog
PIC12FPIC12F629 / 675629 / 675
UsingUsing WatchdogWatchdog
WatchdogWatchdog TimerTimer
provides recovery from a system problem
e.g. a program that goes into an endless loop, or a
hardware problem that prevents the program from
operating correctly
if the program doesn’t reset the watchdog at some
predetermined interval, a hardware reset will be initiated
useful for unattended systems
running both in normal and sleep mode
normal mode – on overflow it initiates RESET
sleep mode – on overflow it initiates wake-up
CLRWDT instruction resets the watchdog timer
Watchdog periodWatchdog periodWatchdog period
a nominal time-out period of 18 ms (with no
prescaler)
a division ratio of up to 1:128 can be assigned to
the WDT under software control by writing to the
OPTION register
-> max. period 2,3s
CLRWDT and SLEEP instructions clear the timer AND
prescaler
Watchdog Timer in CWatchdog Timer in CWatchdog Timer in C
in the header we have to enable or disablein the header we have to enable or disable
watchdog by WDTEN or WDTDISwatchdog by WDTEN or WDTDIS
configuration bits:configuration bits:
__CONFIG(MCLRDIS & WDTEN & INTIO);__CONFIG(MCLRDIS & WDTEN & INTIO);
CLRWDT() macro in C resets watchdog
Watchdog Block DiagramWatchdog Block DiagramWatchdog Block Diagram
WatchdogWatchdog RegistersRegisters
Watchdog registersWatchdog registersWatchdog registers