Saia-Burgess Controls AG
User Manual PCD2.M4x60 │
Document 27-648
│ Edition ENG06 │ 2020-10-21
Watchdog
11-1
11
11
Watchdog relay
PCD2.M4_ CPUs have a hardware watchdog as standard equipment. The watch
-
dog relay is at Pins 5 and 6 at Plug X4.
Technical data
Number of outputs
1
×
relay switching contact
Function
Watchdog function or user output (selectable)
Max. voltage
48 VAC or VDC
Switching capacity
1 A (with DC switch-on voltage, a freewheeling diode should be con
-
nected in parallel to the load)
Functional description
As soon as the watchdog relay is called at the address O 255 by a switch on/
off frequency of < 200ms (or other value configured in device configurator), the
relay contact closes. It remains closed until the pulse time exceeds the configured
value.
Example of an instruction list (IL) sequence:
Label
Command Operand Comment
COB
0
; or 1 … 15
0
STL
WD_Flag
; invert the help flag
OUT
WD_Flag
OUT
O 255
; Output 255 blinking
ECOB
With this code the watchdog triggers even for (continuous) loops that are due to
programming. Regarding user program cycle time, please note the following:
With cycle times longer than 200 ms, the code sequence must be repeated
multiple times in the user program in order to prevent the watchdog triggering
during RUN.
