ProSoft Technology PTQ-PDPMV1 - Manual (Page 209)

PTQ-PDPMV1 ♦ Quantum Platform Hot Standby Support
PROFIBUS DP Master Network Interface Module for Quantum User Manual
ProSoft Technology, Inc. Page 209 of 306
August 12, 2014
Slave Status
Both Masters inform the counterpart of its slave status as a part of the CSI.
The slave status information includes two parts, the SO-bit in register "HSBY
local status", and register "HSBY Nr of local slaves". Based on this information, a
high-level system could switch to the Master that recognize the most slaves.
 The "SO-bit" indicates if the Master recognizes any of its assigned slaves as
offline.
 Register "HSBY Nr of local slaves" indicates how many slaves are online.
How this information is determined depends on if the Master module operates as
active or remote (passive) Master:
 The local (active) Master would use the "state-report" information available
from the Siemens stack. A slave is considered to be online when it
participates in the cyclic Data Exchange sequence.
Note: This means that a slave that reports "Prm-fault" or "Config-fault" is considered to be offline
even if it is physically accessible to the Master.
 The remote (passive) Master would ping all of its assigned slaves with
FDL_Status telegrams once every time it holds the token. A slave is
considered to be online when it responds to the telegram.
During a switchover, the slave status information would be reassembled. This
means that the value of "HSBY Nr of local slaves" and "SO-bit" might dip for a
short while until the "new" local (active) Master has detected its slaves.
Note: This feature affects the performance of the entire network, since the remote (passive) Master
must query all slaves when it holds the token, thus increasing the token rotation time.
Example:
The following illustration shows a network with three slaves and two Masters. MA
is the local (active) Master and MP the passive one.
The table lists the values of the slave status information under different
scenarios.
Note: The only time the slave status information is forwarded to the counterpart is when a slave is
disconnected or fails. In all other cases, the communication link is broken so the information would
not reach the counterpart.