Siemens SINUMERIK 840D sl Function Manual page 1021

Figure 2-3
Basics
Compile-cycle signals
In addition to the standard signals exchanged between the PLC and NCK, an interface data
block for compile cycles is also generated if required (DB9). The associated signals, which
are dependent on the compile cycles, are transmitted cyclically at the start of OB1.
Basic logic functions: PLC Basic program powerline (P3 pl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
PLC/NCK interface
Detailed description
2.6 Interface structure
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