Siemens SINUMERIK 840D sl Function Manual page 1304

Detailed description
2.5 Linking PLC CPUs to 840D
Interface MCP/PLC, interface HHU/PLC (Ethernet link)
MCP/PLC and HHU (HT2) /PLC data exchange takes place via the integrated CP's Ethernet
bus. The CP transfers the MCP/HHU signals to and fetches them from the PLC's internal
DPR (Dual-Port RAM). On the PLC side, the basic program handles communication with the
user interface. The basic-program parameters (FB1, DB7) define the operand areas (e.g.
I/O) and the start addresses.
Interface MCP/PLC (Profibus link)
MCP/PLC data exchange takes place via the PLC's Profibus. The MCP's I/O addresses
must be set in the PLC's process image area and via HW configuration in STEP7. The
MCP*In, MCP*Out pointer variables must be set to the same addresses. The selected DP
slave number must be entered in MCP*BusAdr.
Interface MCP/PLC, interface HHU/PLC (MPI link)
is no longer supported
2.5.4 Diagnostic buffer on PLC
General
The diagnostic buffer on the PLC, which can be read out using STEP7, contains diagnostic
information about the PLC operating system.
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Basic logic functions: PLC basic program solution line (P3 sl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0