Access synchronization by NC-channel

The user expects variable access (read and write) in the temporal sequence as specified in the NC-program. Since NC-program decoding is performed in a planning phase which comes before actual processing of the NC-commands, a variable may not be accessed simply during program decoding but must be accessed synchronously with respect to current program execution (axis movement). This is ensured as follows:

• READ When reading, decoding is halted until current program execution has reached the last decoded NC-program line (implicit FLUSH & WAIT, see also [Programming]). Since a FLUSH & WAIT is not allowed during specified cross-block NC-functionalities (e.g. active spline interpolation, active tool radius compensation), synchronous READ during this functionality is not possible either.
• WRITE Write access is scheduled in the same way as any other NC-command during decoding and is actually performed later during NC machining.

Since this synchronization, in particular halting of decoding in the case of Read access, has undesirable runtime influences, this implicit synchronization can be deactivated when defining the variables. Of course, this is possible only if the instant of read access does not need to be synchronous with processing or if this is ensured anyway by an explicit synchronization point in the NC-program (e.g. explicit FLUSH & WAIT).