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S5-115U Manual
2.6.3
Setting the Scan Monitoring Time
The scan time comprises the duration of the cyclic program. At the beginning of each program
scan, the processor starts a monitoring time (cycle trigger). This monitoring time is preset to
approximately 500 ms. If the scan trigger is not initiated again within this time - for example, as a
result of programming an endless loop in the control program or as a result of a fault in the CPU -
the PLC goes to STOP and disables all output modules. If the control program is very complex, and
the monitoring time can be exceeded, you should restart the monitoring time in the control
program (OB13, see Chapter 11).
There are two possible methods for changing the default scan monitoring time:
•
Initialization in DB1 (see Section 11.3)
•
STEP 5 operations.
You can set the scan monitoring time up to 2.55 s (KF=+255) without having to restart the moni-
toring time.
If you want to change the default scan monitoring time (approximately 500 msec.) via STEP 5
operations, you must transfer a factor for this purpose to system data word 96. The CPU operating
system interprets this factor as a multiple of 10 msec.
Example:
The scan monitoring time is to be set to 100 msec. after every manual cold restart and after
automatic cold restart following power restoration.
The following function block must therefore be called in OB21 and in OB22 with the value "+10".
STL FB2
NAME :ZYKZEIT
DECL :ZEIT
I/Q/D/B/T/C: D
: LW =ZEIT
:
: T
BS
96
: BE
2.7
Accessories
The following subsections give an overview of important accessories for the S5-115U PLC.
EWA 4NEB 811 6130-02b
KM/KH/KY/KS/KF/KT/KC/KG: KF
Load the scan monitoring
time as a multiple of 10 msec.
Transfer time to system
data word 96.
Technical Description
Explanation
2-27
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