Siemens SINUMERIK 840D sl Function Manual page 1145

Brief description of a few important functions
Active/passive operating mode
An online MMC can operate in two different modes:
Active mode:
Passive mode:
After switchover to an NCU, this initially requests active operating mode in the PLC of the
online NCU. If two MMCs are simultaneously connected online to one NCU, one of the two is
always in active and the other in passive operating mode. The operator can request active
mode on the passive control unit at the press of a button.
MCP switchover
As an option, an MCP assigned to the MMC can be switched over at the same time. This
can be done on condition that the MSTT address is entered in parameter "mstt_adress" of
configuration file NETNAMES.INI in the operator panel and MCPEnable is set to TRUE. The
MSTT of the passive MMC is deactivated. so that there is only ever one active MCP on an
NCU at one time.
Boot condition
To prevent the previously selected MCP being reactivated when the NCU is restarted, input
parameters
MCP1BusAdr = 255 (address of 1st MCP) and MCP1STOP =TRUE (deactivate 1st MCP)
must be set when FB1 is called in OB 100.
Releases
When one MCP is switched over to another, any active feedrate or axis enabling signals may
be transferred at the same time.
Note
Keys actuated at the moment of switchover remain operative until the new MCP is activated
(by the MMC which is subsequently activated). The override settings for feedrate and spindle
also remain valid. To deactivate the activated keys, in case of the falling edge of the signal
DB10, ... DBX104.0 (MSTT 1 ready) the input image of the machine control signal is to be
laid on the non-actuated signal level. The override settings should remain unchanged.
Measures for deactivating keys must be implemented in the PLC user program, see example
"Override switchover".
The call is permitted only in cyclic program OB 1.
Basic logic functions: PLC Basic program powerline (P3 pl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0
Operator can control and monitor
Operator can monitor (MMC header only)
Detailed description
2.12 Block descriptions
161