SBC PCD3 Series - Hardware Watchdog Functionality

Saia-Burgess Controls AG
Hardware manual for PCD3 series │ Document 26-789 ENG19│ 2018-06-29
Connections on orange terminal block
PCD3.Mxxx0 Classic CPU and expansion enclosure
3-41
3
3.15.3 Hardware Watchdog
5540
Saia PCD3.M
Saia PCD3Saia PCD3 Saia PCD3Saia PCD3 Saia PCD3Saia PCD3 Saia PCD3Saia PCD3
Terminal 5 and 6 for watchdog relay contact
The PCD3 CPU are equipped with a hardware watchdog as standard. A relay can
be triggered on the I/O address 255 which remains energized as long as the state
of the O 255 changes periodically at least every 200 ms.
FBoxes are available in the PG5 FBoxes for this
purpose.
Function
If for some reason the program part with the Watchdog FBox is no longer
processedinsu󰀩cientlyshortintervals,thewatchdogrelaydropsout.Forfurther
details abour these FBoxes, please read the online help.
The same function can also be realized with AWL. This example works regardless
of the cycle time of the user program.
Example:
COB 0 ; or 1 … 15
0
STL WD_Flag ; invert help ag
OUT WD_Flag
OUT O 255 ; ash watchdog output 255
: :
: :
ECOB
With the code, according to the example, the watchdog drops out in the case
ofinniteloopscausedbytheprogrammer.Thefollowing,however,mustbe
observed with regard to the cycle time of the user program:
For cycle times of more than 200 ms, the code sequence must be repeated
several times in the user program to prevent the Watchdog from dropping in
normal mode.