January 2012 8.37 Linking Files 1749
8.37 Linking Files
You can store the source code of the PLC program in several files. To manage
these files, use the following commands:
USES
GLOBAL
EXTERN
These statements must be located at the beginning of your PLC program—
i.e., before the first PLC command. With the USES statement you link another
file into the program. The GLOBAL statement supplies a label from its own file
for an entry that can be used by all other files. The EXTERN statement
provides a label that is defined in another file and is identified there with
GLOBAL. You can then call this label from the active file. You can dramatically
improve the transparency of your program by dividing your source code by
function into individual groups and then save these groups in individual files.
The number of labels is not limited. You can link up to 256 files to one program.
The total size is only limited by the available memory. If the memory is
exceeded the error message System memory overflow appears. With multiple
files, the main program in the directory must have the "M" status flag. This can
be done in RAM by using the PLC program function "COMPILE" once and
choosing the main program in the file window.
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