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Memory access speeds

Created by: JoshNPS at: 10/6/2020 12:41 PM (10 Replies)

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10/6/2020 12:41 PM	Rate (0)
JoshNPS Regular Member Joined: 10/15/2019 Last visit: 2/2/2023 Posts: 11 Rating: (1)	Hi all, I've been browsing the forum for old post but cannot find any concrete information on what I'm looking for. I've got a S7-1200 1215C PLC and I want to know if there would be any difference in speed if I store all my variables as markers vs storing them in a DB? Would one be quicker than the other? Would it have any effect on the cycle time of the PLC?

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10/6/2020 12:58 PM	Rate (0)
Hati Platinum Member Joined: 9/21/2012 Last visit: 11/6/2024 Posts: 4193 Rating: (472)	JoshNPS Hi all, I've been browsing the forum for old post but cannot find any concrete information on what I'm looking for. I've got a S7-1200 1215C PLC and I want to know if there would be any difference in speed if I store all my variables as markers vs storing them in a DB? Would one be quicker than the other? Would it have any effect on the cycle time of the PLC? You can find the processing times in the system manual of the 1200.

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This contribution was helpful to 2 thankful Users jacek d qwazee

10/6/2020 2:50 PM	Rate (0)
JoshNPS Regular Member Joined: 10/15/2019 Last visit: 2/2/2023 Posts: 11 Rating: (1)	Thank you for your response. I have the manual open but I cannot seem to find the relevant info to answer my question, hence my post here. Can you possibly point me to the correct chapter?

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10/6/2020 3:02 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/6/2024 Posts: 15385 Rating: (2443)	Are you finding your s7-1200 PLC is not performing fast enough and just needs another 1-2% speed increase, or decrease? That's perhaps the order of differences on access times for compiled projects. Siemens recommends staying away from using M-memory and instead use DB's for tags on s7-1200/1500 in their S7-1200/1500 programming manual. If it were significantly slower, they would done something to the compiler to optimize DB memory access. Since M-memory on s7-1200 is an emulation for backwards compatibility with s7-300/400, it might even take longer to access M-tags. JoshNPS Hi all, I've been browsing the forum for old post but cannot find any concrete information on what I'm looking for. I've got a S7-1200 1215C PLC and I want to know if there would be any difference in speed if I store all my variables as markers vs storing them in a DB? Would one be quicker than the other? Would it have any effect on the cycle time of the PLC?
	science guy
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This contribution was helpful to 1 thankful Users JoshNPS

10/6/2020 3:08 PM	Rate (1)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 11/7/2024 Posts: 4932 Rating: (1008)	The use of DBs are more convenient and allow easy transfer from one controller to the next. It is not the fastest. The memory-bit area is the best performing where you need non-optimized (standard) access. It outperforms optimized DBs also, but there are other considerations than pure processing for general problem solving. BR
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This contribution was helpful to 3 thankful Users JoshNPS 0_Einstein Hati

10/6/2020 3:17 PM	Rate (0)
JoshNPS Regular Member Joined: 10/15/2019 Last visit: 2/2/2023 Posts: 11 Rating: (1)	qwazee The use of DBs are more convenient and allow easy transfer from one controller to the next. It is not the fastest. The memory-bit area is the best performing where you need non-optimized (standard) access. It outperforms optimized DBs also, but there are other considerations than pure processing for general problem solving. BR Thank you for this information. This is what I was looking for. Unfortunately I was looking at an older version of the system manual. This information was not in there.

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10/6/2020 3:26 PM	Rate (0)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 11/7/2024 Posts: 4932 Rating: (1008)	JoshNPS Thank you for this information. This is what I was looking for. Unfortunately I was looking at an older version of the system manual. This information was not in there. It is good that you find it useful. The information was available since June 2015. Before that Siemens published execution times without specifying DB access vs not-DB access. Every individual S7-1200 CPU has this specification. Too many small things change from one CPU version to the next. Please keep your manuals downloads up to date.
	Last edited by: qwazee at: 10/06/2020 15:28:02 Activities of this user is voluntary. There is no obligation or liability placed on this user. Though optional, your 'please' and 'thank you' is highly valued.
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10/6/2020 4:05 PM	Rate (0)
JoshNPS Regular Member Joined: 10/15/2019 Last visit: 2/2/2023 Posts: 11 Rating: (1)	qwazee JoshNPS Thank you for this information. This is what I was looking for. Unfortunately I was looking at an older version of the system manual. This information was not in there. It is good that you find it useful. The information was available since June 2015. Before that Siemens published execution times without specifying DB access vs not-DB access. Every individual S7-1200 CPU has this specification. Too many small things change from one CPU version to the next. Please keep your manuals downloads up to date. I had the 2012 manual, now I've downloaded the 2019 version. Thank you.

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10/6/2020 4:32 PM	Rate (0)
0_Einstein Diamond Expert Joined: 7/7/2010 Last visit: 11/6/2024 Posts: 15385 Rating: (2443)	What are those numbers for older firmware versions? That manual is for firmware 4.4 according to the description at the bottom of the screengrab, V4.4 (FW 4.4). Is this the first time Siemens published these specs, or was it also in FW4.2+? As you can tell, I'm not a big fan of caring about things that do not matter that much to me. I try to adhere to the Siemens suggestions for programming practices on the s7-1200/1500, so try not to use too many M-tags. This is easier when using FBs and FCs to handle things and all required parameters are passed into them (rather than accessing global tags from within an FC for example).
	science guy
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10/6/2020 5:50 PM	Rate (0)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 11/7/2024 Posts: 4932 Rating: (1008)	JoshNPS I had the 2012 manual, now I've downloaded the 2019 version. Thank you. Hello. To understand Mr Einstein's point of view, please have a look at.. https://support.industry.siemens.com/cs/#chapter_5343008_0 This leads to a good-to-read document: https://support.industry.siemens.com/cs/document/90885040/ Focus on the memory concept related subjects. BR
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