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Control digital output faster than cycle scan

Created by: SuHu at: 9/3/2019 9:08 AM (8 Replies)

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9/3/2019 9:08 AM	Rate (0)
SuHu Silver Member Joined: 9/8/2016 Last visit: 6/29/2024 Posts: 198 Rating: (10)	Hi, My cycle scan is about 150-160ms. I want to control 4 digital outputs faster than cycle scan. For instance - i want to make my own logic in OB38 (10ms interval) and according to my logic turn on or turn off my digital outputs. Is it possible? I use Step 5.6 and CPU 416-2DP

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9/3/2019 2:22 PM	Rate (1)
CaOd Platinum Member Joined: 5/6/2010 Last visit: 11/5/2024 Posts: 1988 Rating: (279)	Hello Suhu, yes you can do this. You must write in your "normal" program directly to the peripherie. Your address is then e.g.not Q1.0 but PQ1.0 Sorry, but I have actually not a Step7 V5.6 to write it as a example regards CaOd

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This contribution was helpful to 1 thankful Users SuHu

9/3/2019 3:22 PM	Rate (1)
Piotr.M Platinum Expert Joined: 6/24/2013 Last visit: 11/11/2024 Posts: 1652 Rating: (426)	hi it is not allowed to write directly to peripherialbits i.e. pqx0.0 you have 2 options 1. use SFC which writes to peripherial bits 2. buffer whole word or byte to a data block or M bits and then move the said internal tag to PQB /PQW Also beware that monitoring of OB with very short fixed scan time (i.e. 10ms) may cause PLC to go to a STOP mode (observed on S7-300)

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This contribution was helpful to 1 thankful Users SuHu

9/4/2019 8:01 AM	Rate (0)
SuHu Silver Member Joined: 9/8/2016 Last visit: 6/29/2024 Posts: 198 Rating: (10)	Thank you for the answers but still don't understand everything. My CPU has PIQ (Process Image of Outputs) has 2048 bytes and it updates cyclically. My 4 digital outputs are in the middle of PIQ. Let's say Q176.0, Q176.1, Q177.1 and Q177.2 Which SFC should i use? SFC27? I thought that this SFC is allowed to use only when Peripheral Address is used (address greated that 2048 in my case)? If not and i am able to use SFC, could you show me some example? Thank you in advance for help

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9/4/2019 8:30 AM	Rate (1)
mopS04 Platinum Expert Joined: 3/5/2014 Last visit: 8/5/2022 Posts: 5521 Rating: (1054)	hi, process image of Inputs is updated before OB1 and PI of outputs is updated after OB1. When you want to program it in OB38 you need to control it undependend from PI. You can use a Part Process Image(PIP) that can be updatedwith OB38, or you control the I/Os directly with peripherial access or SFC. Peripherial access is e.g. PIB(peripherial input byte) or PQB(peripherial output byte. You can also access words an double-words(PIW/PQW/PID/PQD). Bits can not be accessed in that what. The SFC´s that are mentioned before are DPRD_DAT/DPWR_DAT(SFC14/15). With this functions you can read or write the I/O´s of peripherial devices at the time the function is executed. Step7-help explaines how they work. Also this manual shows you the functions, chapter 16.5/16.6: System Software for S7-300/400 System and Standard Functions Volume 1 and Volume 2 hope this helps, regards,
	FCK WAR! Be nice!
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9/5/2019 11:40 AM	Rate (0)
SuHu Silver Member Joined: 9/8/2016 Last visit: 6/29/2024 Posts: 198 Rating: (10)	Thank you for the answer. After 2 days of searching i want to explain it. I have three options: Option 1: Choose one cyclic interrupt - in my case OB38 - and set one Process Image Partition. For instance PIP1. Go to output module (for instance Q170.0 ... Q170.7) and in hardware settings set Process image to PIP1. That settings cause that ouptuts from Q170.0 to Q170.7 will be updated with the OB38 cycle. Option 2: Control the I/Os directly with peripherial access. If i want to control only Q170.3 with the faster interval i should make a mapping. A Q170.0 = M10.0 A Q170.1 = M10.1 A Q170.2 = M10.2 My own logic = Q170.3 A Q170.4 = M10.4 A Q170.5 = M10.5 A Q170.6 = M10.6 A Q170.7 = M10.7 L MB10 T PQB170 Option 3: Use SFC15 with the similar mapping in Option 2.
	Last edited by: SuHu at: 09/05/2019 11:46:58
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9/6/2019 9:20 AM	Rate (0)
8Noodles Silver Member Joined: 8/3/2017 Last visit: 6/11/2024 Posts: 1086 Rating: (53)	Hi SuHu, and now your issue is solved? Best regards, Noodles
	Please, check out the forum search to find already existing topics regarding your issue and to get some hints.
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9/10/2019 7:53 AM	Rate (0)
SuHu Silver Member Joined: 9/8/2016 Last visit: 6/29/2024 Posts: 198 Rating: (10)	Hello 8Noodles, I have not opportunity to test it on the plant. For sure will come back here with the results.

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9/15/2019 8:55 AM	Rate (0)
SuHu Silver Member Joined: 9/8/2016 Last visit: 6/29/2024 Posts: 198 Rating: (10)	Update. It seems that it is working like it should. Thank you for help.

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