Siemens SINUMERIK 828D Function Manual page 860

P3: Basic PLC Program for SINUMERIK 840D sl
13.6 Coupling of the PLC CPUs
Figure 13-3 NCK/PLC coupling on SINUMERIK 840D (integrated PLC)
NCK/PLC interface
As illustrated in the figure, NCK/PLC data exchange is organized by the basic program in the PLC. At the
beginning of the cycle (OB1), the status information(e.g. "Program running") written to the internal DPR (DPR =
Dual Port RAM) by the NCK is copied to data blocks by the basic program, which the user can then access (user
interface). The control signals for the NCK (e.g. NC start) entered in the interface data blocks by the user are also
written to the internal DPR and transmitted to the NCK at the start of the cycle.
Workpiece-program-specific auxiliary functions transferred to the PLC are first evaluated by the basic program
(interrupt­driven) and then transferred to the user interface at the start of OB 1. If the relevant NC block contains
auxiliary functions that require that NCK processing is interrupted (e.g. M06 for tool change), the basic program
stops the decoding of the NCK block initially 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 only contains auxiliary functions, which do not require interruption of the decoding (e.g. M08
for cooling medium on), the transfer of these "fast" auxiliary functions is directly acknowledged in OB 40, so that
decoding is only insignificantly influenced by the transfer to the PLC.
Basic Functions
860
Function Manual, 09/2011, 6FC5397-0BP40-2BA0