Tasks
The tasks include the following:
1)
•• cold and warm restart,
•• updating the process image of the inputs and outputting the
process image of the outputs,
•• calling the cyclic, time-controlled and interrupt-driven programs,
•• detection and handling of errors,
•• memory management,
•• communication with the programmer (PG).
User interfaces
As the user, you can influence the reaction of the CPU to particular
situations and errors via special interfaces to the system program.
Storing the system program
After switching on the power supply to the PLC (POWER UP) the
system program is read from the EPROM to the internal operating
system RAM.
System program defaults
The following chapters, except for Chapter 7, describe the default
system reaction to process events or errors. Depending on the
defaults, the CPU changes to the stop mode if an operation code error
occurs and the error organization block is not loaded.
Modifying the defaults
You can modify the system response by assigning parameters for the
data block DX 0.
Chapter 7 describes the system response following modification.
1)
When operating with several CPUs (multiprocessing) further tasks are involved.
The Programs in a CPU
CPU 948 Programming Guide
1 - 8 C79000-G8576-C848-04
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