Siemens SINUMERIK 840D sl Function Manual page 1326

Detailed description
2.7 Structure and functions of the basic program
PROFIBUS diagnostics
The slaves of both the Profibus connections MPI/DP or DP1 are registered by the basic
program as group message in the form of a ready signal in the interface signal
• DB10, ... DBX92.0 (MPI/DP Bus Slaves OK) and
• DB10, ... DBX92.1 (DP1 Bus Slaves OK)
to the user program. The group message is derived from the LED status of the respective
Profibus (System state list SZL 0x174).
If an error or a failure of a slave is detected, the alarm 400551 or 400552 is also reported.
The alarm is automatically deleted when the error is removed. Detailed information about the
error or the failure will be displayed in the alarm messages as exact cause of error in a future
HMI software version in the diagnostics. No FC 125, FB 125 is necessary for this diagnostic
display, because the information is called directly from the HMI via the corresponding SZL
functions of the PLC operating system via the communication channels to the PLC. This
saves the relatively large block in the PLC and reduces also the PLC cycle time. Since the
FB 125 works under interrupt disable during its processing, OBs with a higher priority can be
executed more quickly.
Note
Till the HMI software version with the diagnostic display for the Profibus becomes available,
it is recommended to use FC 125 for Profibus diagnostics. This block has relatively less
cycle time and the slave states can be updated via the DB 10 interface signal mentioned
earlier by activating the FC 125 block.
2.7.6 Response to NCK failure
General
During cyclic operation, the PLC basic program continuously monitors NCK availability by
polling the signoflife character. If the NCK is no longer reacting, then the NCK PLC interface
is neutralized and IS NCK CPU ready in signals from NC group (DB 10.DBX 104.7) is reset.
The signals sent by the NCK to the PLC are initialized with default settings.
The PLC itself remains active so that it can continue to control machine functions. However,
it remains the responsibility of the user program to set the machine to a safe state.
52
Basic logic functions: PLC basic program solution line (P3 sl)
Function Manual, 11/2006, 6FC5397-0BP10-2BA0