Siemens SINUMERIK 840Di Function Manual page 930

Detailed description
2.4 Starting up the PLC program
User program
In SW 4 and higher, users can also display the version codes of their own user programs on
the MMC.
For this purpose, a data of type STRING containing a maximum of 54 characters must be
defined in any data block. The data can contain a text of the user's choice. Parameter
assignments for this string are made via a pointer in FB 1. Parameterization requires
symbolic definition of the data block.
References:
/FB1/ Description of Functions, Basic Machine; PLC Basic Program (P3);
Chapter: Block Description
2.4.4 Machine program
The machine manufacturer creates the machine program using the library routines supplied
with the basic program. The machine program contains the logic operations and sequences
on the machine. The interface signals to the NC are also controlled in this program. More
complex communication functions with the NC (e.g., read/write NC data, tool-management
acknowledgments, etc., are activated and executed via basic-program FCs and FBs). The
machine program can be created in different creation languages (e.g., STL, LAD, CSF, S7
HIGRAPH, S7GRAPH, SCL). The complete machine program must be generated and
compiled in the correct sequence. This means that blocks that are called by other blocks
must generally be compiled before the blocks, which call them. If blocks that are called by
other blocks are subsequently modified in the interface (VAR_INPUT, VAR_OUTPUT,
VAR_IN_OUT, VAR) as the program is developed, then the call block and all blocks
associated with it must be recompiled. This general procedure applies analogously to
instance data blocks for FBs. If this sequence of operations is not observed, timestamp
conflicts occur when the data are retranslated into STEP7. In some cases, therefore, it may
not be possible to recompile blocks, creating problems, for example, with the "Block status"
function. It is moreover advisable to generate blocks in ASCIISTL by means of the STEP7
editor when they have been created in the ladder diagram or in single statements
(incremental mode).
2.4.5 Data backup
The PLC CPU does not store symbolic names, only the data-type descriptions of the block
parameters (VAR_INPUT, VAR_OUTPUT, VAR_IN_OUT, VAR) and the data types of the
global data blocks. Without the associated project for this machine, therefore, blocks cannot
be recompiled meaningfully (e.g., for the Block status function or in the event of
modifications subsequently required to PLC CPU programs). It is therefore necessary to
keep a backup copy of the STEP7 project located in the PLCCPU on the machine. This is
extremely useful for servicing purposes and saves time and problems. If the STEP7 project
exists and has been created according to the instructions given above, then symbols can be
processed in the PLCCPU on this machine. It may also be advisable to store the machine
source programs as STL files in case they are required for any future upgrade.
The source programs of all organization blocks and all instance data blocks should always
be available.
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Power Line Basic PLC Program (P3)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0