Systemsoftware
System- and communication configuring D7-SYS - SIMADYN D
2-23
Edition 03.2001
2.1.7 Significance and uses of the process image
A process image is an instantaneous image of all interface signals from
the process at the start of a cyclic task.
For a digital control system, the interface signals must be processed
consistently to the individual processes. In this case, interface signals are
the digital and analog input- or output signals of a hardware module.
The input signals of the various tasks must be kept constant during a
computation cycle. If this was not the case, interface signal changes
while processing a task and run times of the individual function blocks
would unpredictably influence the result of a computation cycle.
The data from the hardware interfaces is processed in the so-called
process image, implemented by the system mode of the function blocks
when a task is started to be processed.
The task administrator (refer to the Chapter "Mode of operation of the
task administrator") of the operating system is started with the basic CPU
clock cycle T0. This decides which tasks are to be started (T1 and a
maximum of additional Tn,
with Tn
ε
{T2...T5}.
Within the task processing, the following components are to be executed:
•
Buffer changeover for the tasks to be started (task 1 T1 and if required
an additional task Tn)
•
System mode of function blocks in T1 corresponding to the block
sequence
•
System mode of function blocks in Tn corresponding to the
block sequence
•
Importing signal interconnections in T1 and standard mode T1
•
Exporting signal interconnections from T1
•
Importing signal interconnections in Tn and the standard mode Tn
•
Exporting signal interconnections from Tn
The components relevant for the process image are highlighted; for the
other components refer to the Chapter "Description and use of the signal
transfer mechanisms".
Necessity for data
consistency
Task processing
