7.1 Application
You can adapt certain system program functions to meet your own
requirements by selecting alternative defaults in DX 0 compared to the
standard defaults (marked in the parameter table by "D").
The defaults of the system program (D) are automatically set during
each COLD RESTART and DX 0 is then evaluated. If you have not
assigned parameters in DX 0 and loaded it, the defaults remain valid;
otherwise the defaults you have selected in DX 0 become the valid
settings.
You can make settings in DX 0 by programming the values just as in
any normal data block (refer to Section 7.2 to 7.4.1) or using the PG
system software S5-DOS from Version 3.0 onwards, you can enter the
values as parameters in a special screen form on your PG (refer to
Section 7.4.2).
You can make use of the full range of functions of the DX 0 screen
form if the PG software STEP 5/ST, Version 6.3 or STEP 5/MT,
Version 6.0 plus the corresponding "Delta diskette CPU 948" is
installed on your PG.
Note
The settings or modifications made in DX 0 only become effective
following a COLD RESTART.
If a modified DX 0 is read during a COLD RESTART, the
unmodified parameter assignments are retained.
Differences compared with
the CPU 946/947
Compared with DX 0 parameter assignment for the CPU 946/947,
there are various differences when assigning DX 0 parameters for the
CPU 948, as follows:
•• Modes:
There is no longer a 150U/155U mode, instead of this, there is
now "interruptability at block boundaries" and
"interruptability at operation boundaries".
•• Processing system interrupts:
With the CPU 948, you can now also combine "process interrupts
via IB 0 = off" (= system interrupt processing) with
"interruptability at block boundaries".
This means that multiprocessor operation is now also possible in
the "interruptability at block boundaries" mode.
•• Additional timed interrupts:
If you switch off the mode "process interrupts via IB 0", the
additional timed interrupts the delayed interrupt (OB 6) and the
clock-controlled interrupt (OB 9) are available.
Application
CPU 948 Programming Guide
7 - 4 C79000-G8576-C848-04
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