Siemens SINUMERIK 828D Function Manual page 838

P3: Basic PLC Program for SINUMERIK 840D sl
13.1 Brief description
Event-driven signal exchange PLC → NCK
An "event­driven signal exchange PLC → NCK" takes place whenever the PLC passes a request to the NCK
(e.g. traversal of an auxiliary axis). In this case, data transfer is also acknowledgment-driven. When performed
from the user program, this type of signal exchange is triggered using a function block (FB) or function call (FC).
The associated FBs (Function Blocks) and FCs (Function Calls) are supplied together with the basic program.
Messages
User messages are acquired and conditioned by the basic program. A defined bit field is used to transfer the
message signals to the basic program, where they are evaluated and, if message events occur, entered in the
PLC's interrupt buffer by means of the ALARM S/SQ functions. If an HMI (e.g. SINUMERIK Operate) is being
used, the messages are transferred to the HMI and displayed.
PLC/HMI data exchange
In this type of data exchange, the HMI takes the initiative, being referred to as the "client" on the bus system. The
HMI polls or writes data. The PLC processes these requests at the cycle control point via the operating system.
The PLC basic program is not involved in these exchanges.
Note
The function of the machine is largely determined by the PLC program. Every PLC program
in the RAM can be edited with the programming device.
838
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Basic Functions