Siemens SINUMERIK 840Di Function Manual page 1219

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
Fig. 2-5
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
PLC/NCK interface
Detailed Description
2.6 Interface structure
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