Introduction "Pointer-Based Communication Blocks; Principle Mode Of Operation; Applications - Siemens SIMATIC FM 458-1 DP User Manual

Configuring
4.5

Introduction "Pointer-based communication blocks"

4.5.1 Principle mode of operation

4.5.2 Applications

Large data
quantities
4-28
Up to D7-SYS Version 6, serial or parallel data transfer operations for
SIMATIC control systems were configured using the so-called "virtual
communication couplings" methods (shown in CFC charts e.g.:
"!VNAME.0001").
Exception: The fiber-optic cable drive coupling SIMOLINK is configured
using special SIMOLINK blocks.
From D7-SYS Version 6, communication links, for example PROFIBUS-
DP, SIMATIC-CPU  FM 458-1 DP as well as for SIMATIC TDC or T400
and SIMADYN D can be alternatively configured using communication
blocks which have become recently available.
In this case, interface data is accessed from the CFC screen using new
blocks, which are inter-connected using a special pointer interface.
Both of these configuring methods (virtual interconnections and pointer-
based communications) can be used together on the same hardware
platform, in the same configuring (application software) and even for the
same interface.
Telegram blocks (CRV_P, CTV_P and S7RD_P, S7WR_P) allow access
to the receiving or to the sending data blocks (telegrams) by providing a
pointer to the particular data block.
This pointer is connected to read/write blocks (DRD..., DWR...).
Together with an offset, a write block can save the data at its input
connection at the required location in the buffer. A read block then
retrieves the appropriate data from the specified location of the receive
buffer and makes it available at its output.
This means that in principle, a virtual interconnection is replaced by a
(read/write) block and a "normal" CFC connection.
Pointer-based communications are especially advantageous where large
amounts of data are involved. For large amounts of data, it is simpler and
faster to configure and change and interconnections are more flexible.
Application Module FM 458-1 DP - User Manual
A5E01078222-02 Edition 03.2009