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Retentivity of DB blocks in S7 300 after power down

9/30/2005 9:17 AM	Rate (0)
BB2 Regular Member Joined: 9/30/2005 Last visit: 11/11/2024 Posts: 15 Rating: (2)	Hello, I observed unexpected behavior of CPU (S7 314 with MMC) after power down. We have an installation with several PLCs (S7). One day we have problems with power supply. Power supply was down and back again in few seconds (in one section of the plant). After power supply was restored in one of the PLCs we lost all actual parameters that were stored in DBs. After that, we tried to turn power off and on for this PLC, but parameters were correctly stored. Do You any idea what could happend there and how to avoid such situations? Regards, BB

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9/30/2005 10:49 AM	Rate (0)
DEBU Posts: 2 Rating: (0)	When I create a new db in my plc project and load it in the cpu it goes into stop mode.But if I load it again in stop mode and reset plc it load into the system.Can I load dbs in run mode?
DEBU Posts: 2 Rating: (0)
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9/30/2005 12:47 PM	Rate (1)
Denilson Pegaia Platinum Member Joined: 9/23/2005 Last visit: 11/11/2024 Posts: 4351 Rating: (1452)	Hello, You can create, or download DB in run Mode. The Stop has probably another cause. To see the real cause of the stop your CPU, please see the diagnostic buffer (STEP 7-> PLC ->Diagnostic/Settings->Module Information) and tell us what is there.
	Denilson Pegaia Siemens Industry Sector Technical Support
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1/7/2006 2:13 PM	Rate (0)
JL Posts: 3 Rating: (0)	We have this problem occuring from time to time on 4 313C cpu's one of them seems to restore initial values after every power of according to that customer. On the other systems so does it happen more rarely, but it happens and often at quick power off and on. The similarity is that all of these systems also has micromaster inverters in the enclousers. Wired by the book!
JL Posts: 3 Rating: (0)
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1/10/2006 1:30 PM	Rate (0)
Chris Silver Member Joined: 8/31/2005 Last visit: 10/24/2024 Posts: 217 Rating: (41)	Hi all! The retentivity behavior of S7 controllers with MMC or without is different. For S7 controllers with MMC DBs are retentive by default. But you can set the retentive behavior for a DB in the properties of the DB (see manual CPU 31xC and CPU 31x, chapter 4.1.3). For controllers without MMC see the manual SIMATIC PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP, chapter 5. This FAQ may also be helpful: S7-300 - Declaring marker areas or data blocks as retentive
	Greetings, Chris
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