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Error Information
PG online function OUTPUT
ISTACK
Online function OUTPUT
BSTACK
5 - 6
You can get information about the status of the control bits and the
contents of the interrupt stack (ISTACK) by using die PG online
function OUTPUT ISTACK.
When the CPU goes into the STOP mode, the system program enters all
the information it requires for a warm restart in the ISTACK. This
information includes:
• • contents of registers,
• • contents of accumulators,
• • STEP address counter SAC
and
• • results codes
Depending on where the interruption leading to the STOP occurred,
the displayed information refers to user blocks or blocks of the system
program (OB 0).
These entries are a valuable aid in error diagnosis.
Before the actual ISTACK is output on the programmer, the status of
the control bits is displayed. The control bits mark the current
operating status and specific characteristics of the CPU and the user
program and provide additional information on the cause of an error.
You can call the ISTACK programmer function not only when the
CPU is in the STOP mode, but also when it is in the RESTART or
RUN mode. However, in the RESTART and RUN modes, you can
only display the control bits (i.e., the first page of ISTACK
information).
The meaning of the control bits and structure of the interrupt stack are
described in detail in Section 5.4.
You can display the contents of the block stack (BSTACK - see
section 3.2 "Nesting blocks") using the PG online function OUTPUT
BSTACK.
The BSTACK contains a listing of all blocks (blocks of the user
program and organization block OB 0 of the system program) called
in sequence and not completely processed when the CPU went into
the STOP mode. Since the BSTACK is filled from the bottom, the top
line of the BSTACK display contains the block that called the block
containing an error.
CPU 948 Programming Guide
C79000-G8576-C848-04
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