Function and characteristics
Any values can be exchanged via external variables between NC (NC-channel), graphical user interface (GUI) and PLC, whereby the variables are handled transparently by the NC, i.e. the significance of the variables is determined purely by the application (NC-program, graphical user interface and PLC). The NC has only the task of transporting these variables and making them available to the user in the NC-program. During the configuration phase, a name, a type and access authorization (write and/or read), in additional to a memory location, are assigned to the external variables. The external variables are configured on the basis of an ASCII list only once during boot-up.
In addition to the simple variables, it is also possible to create one-dimensional fields which are accessed with indexing. The variables can be created in a channel-specific or also cross-channel memory. The values apply throughout the lifetime of an NC-program, i.e. they are not cleared for instance when a new NC-program is started.
There are two options determining the instant of writing/reading a variable from the NC-program:
- Writing/reading of a variable is performed synchronously with current NC-program execution, i.e. the temporal sequence of the NC-commands and variable access operations is ensured.
- Writing/reading of a variable is performed at the time of decoding.
Access via the GUI or the PLC is non-synchronous with respect to NC-program execution.
