PROFIBUS DP-Master

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6.1.5 PROFIBUS_FSPMM_CMD_GET_SLAVE_DIAG_REQ/CNF – Request a
Slave Diagnostic
This packet allows reading out the diagnostic structure of a slave. The desired address of the slave
must be placed in ulRemAdd corresponding to the real address of the slave within the network.
The parameter ulFlags has influence to the kind of execution of this command. The flag
PROFIBUS_FSPMM_GET_DIAG_FLAG_QUERY decides if either the diagnostic data is taken from the internal
buffer of the master without causing a network access to the slave (set flag to 0), or if the service is
sent to the slave directly (set flag to 1) and data of the response is sent back in the answer message.
Calling the command without network access is much faster in reaction time and the preferred method
for getting the answer than the other mode. However, using this mode makes only sense for slaves
that are handled by the master. Only for those slaves the master drives the buffer update mechanism
on every received new diagnostic data. The corresponding bit of each master assigned slave within
the Sl_Diag field in the global bus status field indicates, if a changed diagnostic information since the
last request is available and should be requested and read out. The diag bit of a slave station will be
cleared on each PROFIBUS_FSPMM_CMD_GET_SLAVE_DIAG_REQ that is performed. Sl_Diag-bits of
slaves, which are not assigned to the master, are not influenced by this mechanism in general.
The Sl_Diag field will be updated in relation to the executed main PROFIBUS master cycle time,
which is needed to update all input and output data. If a slave station is permanently not available in
the network for example, then the corresponding diag bit within this field could be set every 500 µsec
repeatedly to indicate that the slave is not present.
PROFIBUS DP-Master |
DOC061001API12EN | Revision 12 | English | 2010-12 | Released | Public © Hilscher, 2006-2010