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Entry type: FAQ Entry ID: 87604432, Entry date: 03/26/2014

FAQ collection for SIEMENS PLC soft redundancy

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FAQ collection for SIEMENS PLC soft redundancy

Question 1: What are the points for attention in hardware configuration?

Answer: Redundancy control of soft redundancy system can only be realized via ET200M, the configuration of which is shown in Fig. 1.The configurations of A and B stations must be the same. Copy the configuration of ET200M, and follow the menu operation in Fig. 2.to complete configuration of station B.

Fig. 1

Fig. 2

Question 2: Which modules support soft redundancy?

Answer: Look up the support list in the soft redundancy manual or refer to the FAQ in the link below.

Question 3: Which of those defined by FC100 "SWR_START" are redundant data areas? And which are non-redundant data areas? What are the differences?

Answer: Redundant sync data area as shown in Fig. 3 includes: process image output area DB/,IEC/M, as the green area shown in Fig. 3. The non-redundant data area includes: DB. Data of the master in the redundant data area is overwritten to the standby station through redundancy link, which ensures master/standby data synchronization; While data in the non-redundant DB area is just transferred in the defined direction A-B or B-A without master/standby tendency. Note: The data area length of either redundancy or non-redundancy of station A must be the same as that of station B, which can be set to 0 if not used.

Fig. 3

Question 4: Effect of DB block in soft redundancy

Answer: Certain DB blocks of particular functions are used in the soft redundancy system, which are defined in FC100 "SWR_START" as shown in Fig. 4

Fig. 4

A: Operation DB of soft redundancy are automatically generated and shouldn't be manually added in the project. DB defined by "DB_SEND_NO" and "DB_RCV_NO" must be the same in both stations.
B: Instance data blocks are defined in FB101 "SWR_ZYK", in which the length of DB5 should be noted. If they are not correctly generated, CPU may work normally but error report arises by SF light, while the diagnostic buffer looks like Fig. 5:

Fig. 5

The length of DB5 in Fig. 6 is found to be only 100 bytes, in which case no inner parameters are displayed when double-clicking and opening DB5, as is shown in Fig. 7.The instance data block thus need to be redefined and regenerated in FB101 "SWR_ZYK" after deleting DB5. 194 bytes of data is transferred in normal MPI synchronization. 358 bytes of data is transferred in Ethernet/PROFIBUS synchronization.

Fig. 6

Fig. 7

C: Redundant data area is where data of the master is being synchronized to the standby station at any time, which needs to be manually created. Instance data block of the IEC Timer need to be generated too, the length of which in station A and B must be the same. Length of the generated DB block should be larger than 2 words (Newly created DB block has length of 2 bytes for it only contains one INT variable).Or else CPU may stop and the diagnostic buffer reports an error as shown in Fig. 8:

Fig. 8

D: Non-redundant DB block

  • need not be manually created and it will automatically generated by the program
  • DB in A-B and B-A directions must be simultaneously used and usage of single direction is forbidden (A-B 0 BYTE, B-A 100 BYTE ----- B STOP; B-A 0 BYTE, A-B 100 BYTE ----- A STOP). Or else, CPU stops and the diagnostic buffer looks like Fig. 9:

    Fig. 9
  • The length in byte of non-redundant DB block must be an even number, not an odd one, as is shown in Fig. 10; the length of non-redundant DB block in station A and B must be the same. Or else, CPU stops and the diagnostic buffer looks like Fig. 11:

    Fig. 10

    Fig. 11

Question 5: Effect of other redundant sync data areas

Answer: The other redundant sync data areas include process image output area and M area, as is shown in Fig. 12. Data of the master is being synchronized to the standby station at any time. Length of the process image output area cannot exceeds the allowed value by CPU, and the maximum length supported by each ET200M slave is 32 bytes; Length of the M area should be larger than 1 byte and smaller than the allowed value by CPU. Or else, CPU stops and the diagnostic buffer looks like Fig. 13. The length can be set to 0 if not used.

Fig. 12

Fig. 13

Question 6: Why does it cause CPU fault when downloading again after changing the parameters in FC100 "SWR_STAT"?

Relevant DB blocks will be generated in FC100 "SWR_START" after CPU starts up. If the old DB blocks were not deleted after parameter changes, it results in CPU fault. The relevant description in the manual is shown in Fig. 14:

Fig. 14

Therefore, following steps are proposed for downloading when changing the parameters in FC100 "SWR_START".

Method 1:
1. Open the online window of project as shown in Fig. 15.
2. Delete all the program blocks following Fig. 15.
3. Download the blocks again as shown in Fig.16.
4. Perform memory reset operation on CPU.

Fig. 15


Method 2:
Select "Blocks" and follow the menu operation in Fig. 17 to download the blocks (delete all the blocks in MMC card, write the new program into MMC card, and reset CPU RAM).

Fig. 17

Question 7: Why does synchronization fail?

When synchronization fails, the return value of FB101 "SWR_ZYK" reports the error of 16#8015 as shown in Fig. 18. Meanwhile the status word DB5.DBX9.5 is set to 1, as is shown in Fig. 19. Check following parameter settings in case of normal physical connection.

Fig. 18

Fig. 19

Check the parameters in FC100 "SWR_START" according to different sync mode as shown in Fig. 20, where "MPI_ADR" denotes the MPI address of the opposite side used in MPI synchronization; "LADDR" and "VERB_ID" are used in PROFIBUS/ETHERNET synchronization, which denote the hardware address and connection number of sync CP respectively, as is shown in Fig. 21.

Fig. 20

Fig. 21

If MPI synchronization is selected, SFC65 "X_SEND" and SFC66 "X_REV" are called by the redundant program block for data synchronization, which occupy connection resource of 2 "S7 basic communication" of S7-300 CPU, as is shown in Fig. 22.Note: enough resources must be preserved in configuration as shown in Fig. 23. Or the communication in synchronization link may be affected due to lack of connection resources.

Fig. 22

Fig. 23

Question 8: Effect of FC102 "SWR_DIAG"

Only when FC102 "SWR_DIAG" is called in OB86, diagnosis of DP bus error would be done by the soft redundancy system so as to perform master/standby switchover operation. Note: If not called, the status word does not report any error and no CPU fault that may lead to master/standby switchover would be caused. In this case, switchover on bus fault of external IM153 modules is performed, but that of soft redundancy system is not. Warning: Block Number of FC102 "SWR_DIAG" must not be modified.

Question 9: Why is the status word not stable and why does DB5.DBX9.5 0-1 flicker?

As is shown in Fig. 24, DB5.DBX9.5 0-1 flickering indicates synchronization sometimes succeeds and sometimes fails. First of all, make sure the length of redundant/non-redundant data areas of both CPU's is the same. Secondly, the master/standby CPU synchronization process is shown in Fig. 25. Data synchronization realizes as FB101 "SWR_ZYK" is successfully executed. Therefore the calling cycle for FB101 "SWR_ZYK" from the two CPU's must be the same. FB101 "SWR_ZYK" should be called in OB35. If called in OB1, make sure the cyclic scan cycles of OB1 are similar.


Fig. 25

If different types of CPU are used in the redundant system, it is suggested to call FB101 "SWR_ZYK" from OB35 instead of OB1. Because different CPU speed may lead to big difference in the cycle time of OB1 which hence affects the synchronization, as is shown in Fig. 26 and Fig. 27.

Fig. 26

Fig. 27

Question 10:.Differences between versions of soft redundancy program package

V1.1 is for the older CPU of CPU315-2DP and S7-400, while libraries of V1.2 are needed to support newer CPU's, as is shown in Fig. 28 (from the manual of redundant software package).

Fig. 28

If fault of PROFINET bus happens in CPU warm start course, V1.2 software would result in CPU stop. The diagnostic buffer looks like Fig. 29. In the V1.3 case, CPU does not stop, SF light is on, BF light flickers and bus error report appears in the diagnosis buffer.

Fig. 29

Question 11: Can soft redundancy data synchronization be realized through the PN interface of CPU unit?

No, it cannot. The program provided in the software package does not support PN interface.

Question 12: Is it possible to integrate a third-party DP slave into the soft redundancy system?

No. Any redundancy control of soft redundancy system can only be realized via ET200M.The slave can be connected to the same PROFIBUS bus, however through which redundancy control cannot be realized. Only the CPU on this bus owes the right of control.

Question 13: Effect of powering down of both IM153 at the same time

Both CPU's are in PROFIBUS fault status, the ET200M station being out of control. The system will perform master/standby switchover once and the status words report error codes, as is shown in Fig. 30. It is hence suggested to use different power supplies for the two IM153 modules.

Fig. 30

Question 14: How to temporarily shut down the ET200M slave without causing master/standby switchover of system?

It generally results in master/standby switchover of redundant system when the DP slave is shut down, with no other measures being taken. Routines avoiding switchover are introduced in the example program below. The routine is selected from the manual and should be called in OB86. I0.0 as switch of switchover avoidance can be input in the operator panel or through other access.

Fig. 31


Note: If I0.0 is set, shutdown of any slave alone will not cause master/standby switchover. The master/standby switchover only happens when more than one slaves shut down. So use this function with caution. After the station recovers, remember to reset I0.0, or system safety will be affected.

Question 15: What about the unused area?

If an area is not used, just set all the parameters in that area to 0. Exception: if the image output area is not used, assign PAA_FIRST a value larger than that of PAA_LAST.

Question 16: Can GSD file be used in ET200M configuration?

It is not recommended to use GSD file for soft redundancy system configuration!

Question 17: How to judge if the redundancy system is working normally?

The soft redundancy system involves redundancy between CPU's and on the DP bus. Observation on the status of "ACT" indicator light of IM153-2 cannot conclude normal operation of the redundancy system. Since switchover between two 153-2's is controlled by the active bus back plane and normal "ACT" status only indicates normal operation of the hardware switchover, not that of the software. Due to that reason the status word of redundancy should also be watched which indicates software switchover status. The redundancy system works normally when both hardware and software switchover are successfully performed.

Question 18: How to configure soft redundancy with TIA Portal V11?

There is no soft redundancy software package that supports TIA Portal V11 at present. TIA Portal V11 thus cannot be used for soft redundancy configuration.

Related reference FAQ:

Wrong area length of soft redundancy in STEP7

Which modules support soft redundancy?

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