Hardware manual PCD1.M2220-C15 │ Document 27-640 – Version ENG03 │ 2020-03-25
Saia-Burgess Controls AG
Watchdog (relay)
CPU/processor unit
3-13
3
3.9
Watchdog (relay)
3.9.1
.. as a watchdog function
With the watchdog circuit, the correct processing of the user program can be
monitored with a higher level of reliability and effective safety measures can be
executed in the case of error.
The PCD1.M2220-C15 CPUs are equipped as standard with this type of hardware
watchdog function, or “watchdog” for short.
The active watchdog, i.e. contact
in operating position (NO-CO), is
displayed by the watchdog LED
lit up in green.
WD
The connections of the watchdog
switchover contact are on plug
X18 (NO, CO and NC) and
assigned to the address
O
255.
Device configuration
See “6.1.4 Digital output” > “Connection assignment for relay output”
Function description
The watchdog electronics monitor the switch-on
flank at O
255. The time lapse starts for the first state
change of O
255 (positive or negative flank) and the
watchdog relay switches to the operating position
(NO-CO).
If no other state change is executed within the set time
(250
ms as standard) at O
255, the watchdog switches
to the rest position (CO-NC).
If the pulse time is exceeded, this can indicate the
following:
-CPU was stopped (no longer in RUN mode)
-Program execution too long
(program too large or AWL program loops)
For the control of O
255 described above, FBoxes are available in the PG5 for this
purpose.
