Siemens SINUMERIK 828D Function Manual page 864

P3: Basic PLC Program for SINUMERIK 840D sl
13.7 Interface structure
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 (DB 9). The associated signals, which are dependent on the compile cycles,
are transmitted cyclically at the start of OB 1. The basic program starts transmission at the lowest address and
works up to the highest. First, signals are transferred from the PLC to the NCK, then from the NCK to the PLC.
The user must synchronize the NCK and PLC as necessary (e.g. using the semaphore technique). Signal
transmission is asynchronous between NCK and PLC. This means, for example, that active NCK data
transmission can be interrupted by the PLC. This can mean that data is not always consistent.
PLC/NCK signals
The group of signals from the PLC to NCK includes:
• Signals for modifying the digital and analog I/O signals of the NCK
• Keyswitch and emergency stop signals
Figure 13-5 PLC/NCK interface
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Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Basic Functions