PC Control / Profi Control 645-12M Instruction Manual pdf - Kuhnke

4.5.2. External operands as process image
PC Control 645-12M used as PLC
External operands are read as inputs or controlled as outputs
via PROFIBUS. There are various sources and destinations:
- - decentralised input/output devices (e.g. Profi I/O 690E)
- - other programmable logic controllers with a DP slave interface
- - positioning controllers, etc.
As a gate to PROFIBUS, there is a 7 kbyte RAM memory
available to PC Control 645-12M for the external operands
(3 kbyte bit-addressable, 4 kbyte byte-addressable).
This memory represents the process image of the available
external operands.
VEBES creates a list of the external operands
VEBES (see instruction manual E 315 GB, VEBES) is used
for network configuration. This process creates projects for
all participating Kuhnke masters which are then programmed
/ edited with the KUBES functionality. During network
configuration with VEBES, the programmer determines
the communication partners and the amount of communication
objects (external operands). VEBES adds these
external operands to the list of operands in the corresponding
project and distributes them within the process image
memory. During programming, they can then be addressed
like local operands. It is also possible to use mnemonics in
the symbol table.
PROFIBUS updates the process image
During operation, PROFIBUS automatically takes care of
transmitting data between communication partners and
process image as often as possible. As this is done at certain
time intervals and controlled by interrupts, up-dating
may also occur while a (program) module is being processed.
This is why PROFIBUS process image data may be different
at the beginning and the end of a module (see chapter
"4.9.1. Data consistency by OC_CRIT"). This does not apply
to interrupt and timer modules.
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