Siemens SIMATIC S5 Manual page 213

Blocks
Optimization of Call Frequency
Establish which functions you require frequently
Draw up a diagram of the PLC cycle and mark all calls
- on their individual axis and
- on a shared axis
Example:
The following are used for a PLC cycle time of 300 ms, (user program 200 ms, operating system 100
ms)
a every 160 ms User timer updating
b every 30 ms Interrupt handling (OB 2) and time OB processing (OB 13)
c every 100 ms Programmer input processing
d every 120 ms SINEC L1 processing
a
b b b
b
c c c
c
d d d
d
BS 115F
FB 254 is called 8 times per cycle.
6-12
a
b
b
c
c
b b
d
d
160 ms
a User timer updating
30ms
b Interrupt handling and
time-interrupt OB processing
100 ms
c Programmer input processing
120 ms
d SINEC L1 processing
Figure 6-2. FB 254 Calls (Ideal Schematic)
b
b c d b a
User program (8 calls)
S5-115F Manual
a
b
c
b d
t
BS 115F
t
t
t
t
EWA 4NEB 811 6149-02