Technical data

2.4.3
Special Data Blocks
On the CPU 948 data blocks DB 0, DB 1, DX 0, DX 1 and DX 2 are
reserved for special functions. They are managed by the system
program and you cannot use them freely for other functions.
DB 0
•• Data block DB 0 (see Section 8.3.2)
Data block DB 0 contains the address list with the start addresses
of all blocks that are located in the data block RAM of the CPU.
The system program generates this address list during
initialization (following each POWER UP or OVERALL RESET)
and it is updated automatically when you use a programmer to
change data blocks or generate a new data block.
DB 1
•• Data block DB 1 (see Section 10.1.6)
Data block DB 1 contains the list of digital inputs/outputs (P
peripheral with relative byte addresses from 0 to 127) and the
interprocessor communication (IPC) flag inputs and outputs that are
assigned to the CPU. If applicable, the block may also contain a timer
field length.
DB 1
can have parameters assigned and be loaded as follows:
to reduce the cycle time in single processor operation, since
only the inputs, outputs or timers entered in DB1 are updated.
DB 1 must be assigned parameters and loaded as follows:
a) for multiprocessing
b) when IPC flags exist with CPs
DB 2
•• Data block DB 2 (see Section 4.4.3)
You use data block DB 2 to assign parameters to the closed loop
controller structure R64. The closed loop control function can be
ordered as a software product and operates supported by the
system program.
2
Data Blocks
CPU 928B Programming Guide
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