Siemens SINUMERIK 840Di Function Manual page 1238

Detailed Description
2.7 Structure and functions of the basic program
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).
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, project-related 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 bits to 32bit REAL. The maximum precision of 32bit REAL numbers is
approximately 10 to the power of 7.
2-44
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0