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Find OBs Execution time

Created by: Nurmard at: 8/31/2023 7:54 AM (5 Replies)

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8/31/2023 7:54 AM	Rate (0)
Nurmard Posts: 15 Rating: (0)	Hello, I would like to know exactly how long it takes for a program written in one of the organization blocks (like OB1 or OB35 ) on the S7-300 to run. Where can I see it in the Step Seven Simatic Manager software? Most of the answers I saw in different forums did not answer my question, or maybe I didn't understand it correctly, because this program execution time will definitely vary for each program, and the answers I found were a general model. I will be glad if you can guide me.
Nurmard Posts: 15 Rating: (0)
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8/31/2023 8:34 AM	Rate (0)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 12/11/2025 Posts: 5656 Rating: (1083)	Nurmard Hello, I would like to know exactly how long it takes for a program written in one of the organization blocks (like OB1 or OB35 ) on the S7-300 to run. Where can I see it in the Step Seven Simatic Manager software? Most of the answers I saw in different forums did not answer my question, or maybe I didn't understand it correctly, because this program execution time will definitely vary for each program, and the answers I found were a general model. I will be glad if you can guide me. You will need to add some coding into the program to do the task. There is no function in Step7 that gives us a breakdown of the cycle time contribution for each block. We only have the total cycle time. Find some general information: How do you measure the time in STEP 7 V5.x? Focus on use of the TIME_TCK instruction.
	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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8/31/2023 12:10 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 1/14/2026 Posts: 5155 Rating: (772)	You must be aware that in case of S7-300 CPUs time measurement resolution is 1 ms. Usually it is completely useless for measuring runtimes of interrupt routines or parts of a code.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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8/31/2023 5:16 PM	Rate (0)
qwazee Platinum Expert Joined: 3/30/2020 Last visit: 12/11/2025 Posts: 5656 Rating: (1083)	jacek d You must be aware that in case of S7-300 CPUs time measurement resolution is 1 ms. Usually it is completely useless for measuring runtimes of interrupt routines or parts of a code. I did loose sight of the detail you mention. Thanks for pointing out the flaw in my suggestion. Do I understand you correctly?.. There is no way to measure the execution duration of a code block.
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9/4/2023 12:02 PM	Rate (0)
jacek d Platinum Expert Joined: 9/23/2005 Last visit: 1/14/2026 Posts: 5155 Rating: (772)	qwazee Do I understand you correctly?.. There is no way to measure the execution duration of a code block. Not within code itself nor any software tool I know of. Runtimes can be measured to some extent by direct access to digital output from code and measuring that output. But even fast digital outputs have internal cycle time of 20 us. Also output rise/fall times should be accounted for. Personally I was rather using calculations than measurements. After few such exercises I got intuition about do's and don'ts as well as worked out some tricks to improve runtimes.
	Regards, Jacek What is confusing you is the fact that you never see a number but always its digit representation. So you end up thinking that the number is the representation. - Andrej Bauer Any claims against me - based on whatever legal reason - resulting from the use of any code and/or ideas presented on this forum shall be excluded. #StayWithUkraine
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This contribution was helpful to 1 thankful Users qwazee

9/6/2023 10:04 AM	Rate (0)
bit7 Bronze Member Joined: 7/26/2008 Last visit: 1/12/2026 Posts: 110 Rating: (20)	Hi Nurmard, for a rough estimate I would call the function in a loop 10, 100, 1 000 times and use the change in scan time for calculation.

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