Siemens SIPROTEC Manual page 37

Two PROFIBUS DP
modules
Event list mecha-
nism and redun-
dancy
SIPROTEC PROFIBUS DP - Bus mapping 6MD662/3/4
C53000-L1840-B011-03
The read entries then will be deleted from the event list buffer on the PROFIBUS DP
module and the next (max. three) entries can be copied to the input telegram and sent
to the master with an incremented sequence number.
Two event lists (one on each module) exist in a redundant PROFIBUS DP slave with
two PROFIBUS DP communication modules in a SIPROTEC device.
Indication changes are transferred to both modules and there are entered in the event
list as well as in the input telegram to the master (including an incremented sequence
number).
But only one module can evaluate the confirmation that the master has read the event
list entries because (according PRIMARY/BACKUP concept)
• only one of the PROFIBUS DP modules has the PRIMARY state,
• output data from the master are only evaluated in PRIMARY state.
Therefore, an additional internal acknowledgement way exists from the PRIMARY
module to the BACKUP module via RedCom for event list entries which were read by
the PRIMARY master.
The behavior of the event list mechanism in a redundant system is explained in the
following.
To this we assume as a starting point that the event lists on the two modules do not
contain any entries.
1. An indication change is transferred to both PROFIBUS DP modules by the
SIPROTEC device.
Every indication gets an unique (internal) identification number before transmis-
sion which also is transmitted to the modules.
2. The PROFIBUS DP modules enter the indication change into the event list buffer,
copy it in the associated area of the input telegram and increment the sequence
number.
3. Both PROFIBUS DP masters recognize that a new event list entry is transmitted.
They read the entry and copy the sequence number in the output telegram.
4. After the sequence number receipt from the master is received, the PRIMARY
slave module deletes the entry from its event list buffer.
Because the BACKUP slave module does not evaluate the output data from the
master, the entry there remains in the event list buffer and in the input telegram.
5. The PRIMARY module now sends via RedCom a receipt to the BACKUP module
that this event list entry was read and evaluated in the PRIMARY sub-system and
therefore also can be deleted in the BACKUP sub-system (Event List Delete, ref.
to Table 1-7).
In the RedCom telegram, the (internal) identification numbers serve as references.
6. The BACKUP slave module now deletes the entry which was indicated in the Red-
Com telegram from its event list buffer.
7. PRIMARY and BACKUP modules now check whether further entries exist in their
event list. The next (max. three) entries then can be copied in the input telegram
(including incrementing of the sequence number).
Redundant PROFIBUS DP interface
37