Siemens SINUMERIK 840D sl Function Manual page 1017

NCK/PLC interface
The data exchange NCK/PLC is organized on the PLC-side by the basic program.
The Status information stored by the NC in the internal Dual–Port–RAM (DPR) (such as
"Program is running") are copied by the basic program in the data blocks at the start of the
cycle (OB 1), which the user can then access (user interface). The user also enters NC
control signals (e.g. NC start) in the interface data blocks, and these are also transferred to
the NC at the start of the cycle.
Auxiliary functions transferred to the PLC dependent on the workpiece program are first
evaluated by the basic program (alarmdriven) and then transferred to the user interface at
the start of OB1. If the relevant NC block contains auxiliary functions that require the
interruption of the NC machining process (e.g. M06 for tool change), the basic program halts
the execution of the block on the NC for one PLC cycle. The user can then use the "read
disable" interface signal to halt the block execution until the tool change has been
completed. If, on the other hand, the relevant NC block does not contain auxiliary functions
requiring the interruption of the NC machining process (e.g. M08 for "Cooling on"), the
transfer of these "rapid" auxiliary functions is enabled directly in OB 40, so that block
execution is only marginally influenced by the transfer to the PLC.
The evaluation and enabling of the G functions transferred from the NCK are also alarm-
driven, however they are transferred directly to the user interface. Where a G function is
evaluated at several points in the PLC program, differences in the information of the G
function within one PLC cycle may arise.
In the case of NC actions triggered and assigned with parameters by the PLC (e.g. traverse
concurrent axes), triggering and parameter assignment is performed using FCs and FBs, not
interface data blocks. The FCs and FBs belonging to the actions are supplied together with
the basic program. The FCs must be loaded by the user and called in the PLC program of
the machine manufacturer (machine program). You can find an overview of the FC, FB and
DB blocks, grouped according to their basic and extended functions, in:
References::
/FB1/Function Manual, Basic Functions; PLC Basic Program (P3);
"PLC program commissioning"
OP/PLC interface
Data are exchanged between the OP and PLC via the OP/NC serial bus, COM module and
C bus. The COM module transfers the data intact from one bus segment to another. It
merely converts the baud rate. The OP is always the active partner (client) and the PLC is
always the passive partner (server). Data transmitted or requested by the OP are read from
and written to the OP/PLC interface area by the PLC operating system (timing: cycle control
point). From the viewpoint of the PLC application, the data are identical to I/O signals.
MCP/PLC interface, HHU/PLC interface (840D only)
Data are exchanged between MCP/PLC and HHU/PLC via the serial bus MCP, HHU/NC,
COM module, and NCK. The NCK transfers the MCP/HHU signals to and fetches them from
the internal NC/NCK DPR (dual-port RAM). On the PLC side, the basic program handles
communication with the user interface. The basic program parameters define the operand
areas (e.g. I/O) and the start addresses.
Basic logic functions: PLC Basic program powerline (P3 pl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Detailed description
2.5 Linking PLC CPUs to 810D, 840D
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