Siemens SIMATIC Manual page 31

Various Call Options for Pulse Control (SELECT)
In a fast process, extremely short pulse generator sampling times (for example 10
ms) are necessary. Due to the program run time (CPU utilization) it is not practical
to process the control sections in the same cyclic interrupt OB as the calculation of
the pulse output. You then either move the control functions to OB1 or to a slower
cyclic interrupt OB (S7-400).
The following table provides an overview of the parameter settings for the SELECT
input parameter:
Application
Default situation: The pulse
generator sampling times
are not particularly short on
the S7-300 and S7-400
(for example CYCLE_P =
100 ms)
Short pulse generator
sampling times on the S7-
300
(for example CYCLE_P = 10
ms)
Short pulse generator
sampling times on an S7-
400
(for example CYCLE_P = 10
ms)
Note
If you implement the processing of controller functions and pulse generator with
two block calls, note the following:
•
The process value (PV_IN or PV_PER) must be supplied with a value when
the pulse generator is called. All other formal operands can be supplied with
values when the controller functions are called.
•
The SELECT parameter must be supplied with a value at every call.
•
If you locate the call in OB1 with SELECT = 1, you implement the conditional
call in the example "pulse controller, OB 35, OB 1".
PID Temperature Control
A5E00125039-02
Continuous Temperature Controller FB 58 "TCONT_CP"
Block Call
Call in cyclic interrupt OB
with SELECT = 0
Conditional call (QC_ACT =
TRUE) in OB1 with SELECT
= 1
Call in cyclic interrupt OB
with SELECT = 2
Call in slow cyclic interrupt
OB with SELECT = 3
Call in fast cyclic interrupt
OB with SELECT = 2
Functionality
Control section and pulse
output in the same cyclic
interrupt OB
Control section in OB1
Pulse output in cyclic
interrupt OB
Control section in slow cyclic
interrupt OB
Pulse output in fast cyclic
interrupt OB
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