P3: Basic PLC Program for SINUMERIK 840D sl
13.8 Structure and functions of the basic program
Basic Functions
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
883
ASUBs
Asynchronous subprograms (ASUBs) can be used to activate any function in the NCK. Before an asynchronous
subprogram can be started from the PLC, it must be ensured that it is available and prepared by the NC program
or by FB 4 PI services (ASUB).
Once prepared in this way, it can be started at any time from the PLC. The NC program running in one of the
parameterized channels of FC 9 is interrupted by the asynchronous subprogram. An ASUB is started by calling
FC 9 from the user program by setting the start parameter to 1.
Read/Write NC variables
NCK variables can be read with FB GET while values can be entered in NCK variables with FB PUT. The NCK
variables are addressed via identifiers at inputs Addr1 to Addr8. The identifiers (symbols) point to address data,
which must be stored in a global DB. To allow generation of this DB, PC software is supplied with the basic
program with which the required variables can be selected from a table, which is also supplied. The selected
variables are first collected in a second, projectrelated list. Command Generate DB creates a "*.AWL" file, which
must be linked to the program file for the machine concerned and compiled together with the machine program.
1 to 8 values can be read or written with a read or write job. If necessary, the values are converted [e.g. NCK
floating point values (64 bits) are converted to PLC format (32 bits with 24-bit mantissa and 8bit exponent) and
vice versa]. A loss of accuracy results from the conversion from 64-bit to 32bit REAL. The maximum precision of
32bit REAL numbers is approximately 10 to the power of 7.
Note
If an asynchronous subprogram has not been prepared by an NC program or by FB 4
(ASUB) (e.g. if no interrupt no. has been assigned), a start error is output (StartErr = TRUE).
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