Technical data

OUTPUT ISTACK
programmer online function
You can get information about the status of the control bits and the
contents of the interrupt stack (= ISTACK) using the ISTACK
programmer online function.
When the CPU goes over to the STOP mode, the system program
enters the following information in the
ISTACK. This information is
required for a warm restart:
•• register contents
•• accumulator contents
•• STEP 5 address counter SAC
and
•• condition codes
These entries can be very helpful for 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 certain characteristics of the CPU and the user
program and provide additional information on the cause of an error.
You can use the "Output ISTACK" function in the STOP, RESTART
and RUN modes; however, in RESTART and RUN you only get
information via the control bits and not via the contents of the
ISTACK.
The meaning of the control bits and the structure of the interrupt stack
are described in more detail in Section 5.3.
System data RS 3 and RS 4 If your CPU returns to the stop mode owing to an error during the
RESTART, the cause of the error is defined in greater detail in the
system data words RS 3 and RS 4 (see Section 5.5). These involve
errors detected by the system program when it sets up the address list
in DB 0 or evaluates DB 1, DB 2, DX 0 or DX 2.
Error Information
CPU 928B Programming Guide
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