Siemens SINUMERIK 840Di Function Manual page 1194

Brief Description
Event-driven signal exchange PLC → NCK
An "event-driven 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
function. Where an HMI (e.g. HMI embedded) is provided, the messages are transferred to
and displayed on the HMI.
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 HIM 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.
1-2
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0