Different Cycle Times - Siemens SIMATIC S7-400 Manual

Cycle and Response Times of the S7-400

9.3 Different cycle times

9.3 Different cycle times
Fundamentals
The length of the cycle time (T
different cycle times, T
OB 1 is interrupted by a time-of-day interrupt OB (here, OB10).
PIQ
Upda-
ting
Figure 9-2
Fluctuation of the block processing time (e.g. OB 1) may also be a factor causing cycle time
fluctuation, due to:
● Conditional commands
● Conditional block calls
● Different program paths,
● Loops, etc.
Maximum Cycle Time
You can modify the default maximum cycle time in STEP 7 (cycle monitoring time). When
this time has expired, OB 80 is called. In OB 80 you can specify how the CPU is to react to
time errors. If you do not retrigger the cycle time with SFC43, OB 80 doubles the cycle time
at the first call. In this case, the CPU goes to STOP at the second call of OB 80.
If there is no OB 80 in the CPU memory, the CPU goes to STOP.
9-6
cyc
and T
cyc1
Current cycle
T
cyc 1
PII
Upda-
OB1 SCC
ting
Different cycle times
) is not identical in each cycle. The following figure shows
. T is longer than T
cyc2 cyc2
Next cycle
T
cyc 2
OB10
PIQ PII
Upda- Upda-
OB1
ting ting
, because the cyclically scanned
cyc1
Next cycle but one
PIQ
Upda-
OB1 SCC
ting
S7-400 Automation System, CPU Specifications
Manual, 10/2006, 6ES7498-8AA04-8BA0
PII
Upda-
ting