Hardware Manual PCD 1 / PCD 2 Series│Document 26 / 737│Edition EN 15│2008-07-22
Saia-Burgess Controls AG
Monitoring the CPU (watchdog)CPUs and expansion housings3
3.17.2 PCD2 hardware watchdog
PCD2 CPUs are fitted with a hardware watchdog as standard. A relay at I/O address
255 can be triggered; this remains activated as long as the status of O 255 changes
periodically at least every 200 ms. Within PG5, FBoxes are provided for this purpose.
If for any reason the program component with the watchdog FBox is no longer be-
ing processed at sufficiently short intervals, the watchdog relay will drop out and the
yellow watchdog LED will go out. Please read online help for more details on these
FBoxes.
The same function can also be implemented with IL (AWL) instructions. There are
various ways of doing this:
Example:COB 0 ; or 1 ... 15
0
STL WD_Flag ;Invert help flag
OUT WD_Flag
OUT O 255 ;Set output 255 to flashing
: :
: :
ECOBWith the code shown in example, the watchdog drops out in the case of loops caused
by the programmer. With regard to the cycle time of the user program, please note:
With cycle times of more than 200 ms, the code sequence must be repeated
several times in the user program, to prevent a drop-out of the watchdog in normal
operation.As address 255 is in the normal I/O range, there are restrictions on the permissible
I/O modules in certain sockets:CPU type Restrictions
PCD2.M110 none
PCD2.M120/M150 1) No analogue, counter and motion control modules on the
socket with base address 240
2) Output 255 cannot be used for digital I/O modules either
PCD2.M170 1) No analogue, counter and motion control modules on the
sockets with base addresses 240 and 496
2) Outputs 255 and 511 cannot be used for digital I/O modules
either
PCD2.M480 1) No analogue, counter and motion control modules on the
socket with base address 240
2) Output 255 cannot be used for digital I/O modules either
The status of the watchdog is displayed by the yellow "WD" LED:
LED lit up: Relay closed
LED not lit up: Relay dropped out