Technical data

If you do not want to program the corresponding organization block,
you can prevent the transition to the STOP mode by assigning
appropriate parameters to
data block DX 0.
Interruptions during
processing of error
organization blocks
After the system program calls the appropriate organization block, the
user program in that block is processed.
If another error occurs while the first organization block is being
processed, the program is interrupted at the next operation boundary
and the appropriate second organization block is called, just as in
cyclic program execution.
The organization blocks are processed in the order in which they are
called. The nesting depth for error organization blocks depends on the
following:
•• The type of error
No organization blocks belonging to the same program processing
level can be nested within each other. (See Chapter 6 for the
assignment of error OBs to the program processing level).
When processing OB 27 (program processing level BCF) it is, for
example, possible to nest OB 32 (program processing level LZF),
however, OB 29 or OB 30 (also BCF) cannot be nested in OB 27.
If two blocks from the same program processing level are called,
the CPU changes immediately to the STOP mode.
•• The number of program processing levels currently active at
any one time
For each activated program processing level, the system program
requires extra memory space to set up the ISTACK when an
interrupt occurs. If there is not enough memory left, an ISTACK
overflow results.
If there is an ISTACK overflow, the CPU changes immediately to
the STOP mode.
•• The number of blocks called at any one time
If there is a BSTACK overflow, the CPU changes immediately to
the STOP mode.
5
Error Handling using Organization Blocks
CPU 928B Programming Guide
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