Watlow Electric Revision 5 - Manual (Page 20)

15
3.2.2 COMMUNICATIONS WATCHDOG TIMER
The communications timer provides a method of turning off all control
outputs if there is a problem in the host computer that effects
communication. It operates by monitoring activity on the communication
line. If this controller has not been contacted within the time interval, it
automatically sets all control outputs to manual with zero outputs. A
dedicated digital output is set when the watchdog times out.
WARNING: IF THE COMMUNICATIONS WATCHDOG IS
ENABLED, INSURE THAT THE HOST COMPUTER
COMMUNICATES WITH EACH SYSTEM 32 WITH IN THE TIME
LIMIT. IF NOT THE CONTROL OUTPUTS WILL BE SET TO
MANUAL WITH ZERO OUTPUT.
Switch Setting Watchdog Status
On Enabled
Off Disabled
The hardware bit switch number 5 must be set to the "ON" position to
enable the communications watchdog timer. If the switch is ON at startup
then the controller constantly monitors the elapsed time between host
communication packets and takes action should the elapsed time overflow
the preset timeout period.
Furthermore, the option may be disabled by the host. If a value of -1 is
written into the timeout period counter then the controller disables the
option and ceases to monitor elapsed time. To re-enable the option via
software, the host must rewrite a valid timeout period to the watchdog
counter.
Timeout Period
The host computer may adjust the timeout period value within the range of
1 to 1092 seconds (or 18.2 minutes) with a resolution of one second. A 2-
byte number representing the length of the timeout period in seconds can be
written to the controller data table addresses 0290 and 0291 Hex.
The default timeout period (set by the controller on startup/reset) is 2
minutes (120 seconds).
Controller Action on Timeout
If the watchdog option is enabled and the elapsed time between
communication packets from the host exceeds the set timeout period, the
controller initiates a communications alarm sequence. This sequence
involves the following :