WATCHDOG TIMER
SECTION 11
Page 11-1 RPC-320
DESCRIPTION
The watchdog timer is used to reset the RPC -320 if the
program or CPU "crashes" . The time r is built into the
80C320 CP U. Timed access requirem ents built into the
CPU make it high ly unlikely an er rant pr ocessor would
cancel a watchdog timer.
The watchdog should not be used in loops which do not
end quickly or ar e of indetermina te duration unless a
WDOG command is included. An example of an
indeterminate loop is one that waits for a port condition
to change.
The timer is set by executing a WDOG
n
command.
n
is
0, 1, or 2. 0 turns off the timer. 1 sets the watch dog
time to 380 ms while 2 sets it to 2.8 seconds. Executing
WDO G by itself resets the timer. WD OG must be
executed pe riodically to p revent a reset.
When the watchdog times out, a softwar e reset is
perfor med. The effe ct is lines at J3 do not ch ange as in
a power-up or har dware reset. Lines at P6, display, and
keypad port ar e reset to power -up conditions.
EXTERNAL RESET
The card is reset externally by mom entarily shorting
W10[1- 2]. R eset is also achiev ed by shor ting W10-2 to
ground. Maintain this short for at least 10 ms. The card
will then reset for abo ut 350 ms.