Siemens SINUMERIK 840Di Function Manual page 937

Fig. 2-2
NCK/PLC interface
NCK/PLC data exchange is organized by the basic program in the PLC.
The status information (e.g., "Program running") stored in the internal DPR is copied to data
blocks by the basic program at the beginning of the cycle (OB1), which the user can then
access (user interface). The user also enters NC control signals (e.g., NC start) in the
interface data blocks, and these are also transferred to the NC at the start of the cycle.
Auxiliary functions transferred to the PLC dependent on the workpiece program are first
evaluated by the basic program (alarmdriven) and then transferred to the user interface at
the start of OB1. If the relevant NC block contains auxiliary functions that require the
interruption of the NC machining process (e.g., M06 for tool change), the basic program halts
the execution of the block on the NC for one PLC cycle. The user can then use the "read
disable" interface signal to halt the block execution until the tool change has been
completed. If, on the other hand, the relevant NC block does not contain auxiliary functions
requiring the interruption of the NC machining process (e.g., M08 for "Cooling on"), the
transfer of these "rapid" auxiliary functions is enabled directly in OB 40, so that block
execution is only marginally influenced by the transfer to the PLC.
The evaluation and enabling of the G functions transferred from the NCK are also alarm-
driven, however they are transferred directly to the user interface. Where a G function is
evaluated at several points in the PLC program, differences in the information of the G
function within one PLC cycle may arise.
Power Line Basic PLC Program (P3)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
NCK/PLC connection on 810D, 840D (integrated PLC)
Detailed description
2.5 Linking PLC CPUs to 810D, 840D
2-25