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Reactions to interrupts
and errors
To allow you to specify the reactions to interrupts or errors, special
organization blocks (OB 2, OB6 and OB9 to OB 18 for interrupt
servicing, OB 19 and OB 23 to OB 35 for reactions to errors) are
available on the CPU 928B. You can store an appropriate STEP 5
program in these blocks.
When interrupts or errors are to be processed, the system program
activates the corresponding organization block during cyclic
processing. This means that the cyclic processing is interrupted to
service an interrupt or to react to an error. The nesting of the
organization blocks has a fixed priority (for further information, refer
to Chapters 4 and 5).
In addition to the organization blocks, you can also influence the
reaction of the CPU to interrupt servicing by assigning parameters in
data block DX 0.
Organization blocks OB 1 to OB 39 can be called by the system
program as soon as they are loaded in the program memory (
also
during operation
).
If the OBs are not loaded, there is either no reaction from the CPU or
(in the event of errors) it goes to the stop mode (refer also to
Section 5.4).
You can also load data block DX 0 into the program memory during
operation like the organization blocks.
It is, however, only effective
after the next COLD RESTART.
If DX 0 is not loaded, the standard
settings apply (refer to Chapter 7).
3.4.1
Definition of Terms used in
Program Execution
Cycle time
The cycle begins when the cycle monitoring time is triggered and
ends with the next trigger. The time that the CPU requires to execute
the program between two triggers is called the cycle time. The cycle
time consists of the runtime of the system program and the runtime of
the user program.
The cycle time therefore includes the following:
•• the time required to process the cyclic program (system and user
program),
•• the time required to process interrupts (e.g. time-controlled
interrupt),
•• the time required to process interruptions (errors).
Processing the User Program
CPU 928B Programming Guide
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