2/21/2021 4:30 PM | |
Joined: 9/27/2006 Last visit: 9/18/2024 Posts: 12282 Rating: (2684)
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Hello sarunas.z; You are using a Wago Profibus coupler to connect the 750-404 counter to the S7 CPU? Let's see if I can explain how this works with the help of the screenshot below. The left part of the screenshot is from this 750-404 manual, which you can download from this link: https://www.wago.com/global/d/1264 As you can see the data you need to read from the 750-404 counter occupies 5 bytes, one command/status byte followed by a 32-bit counter value, over 4 bytes. To read a dword value from a fieldbus (such as Profibus) you must read all the bytes from the counter as a single 5-byte unit, not each byte individually. Siemens names this "consistent data", and you must use SFC 14 to read consistent data from a Profibus slave or Profinet IO-Device.. The second part of the screenshot comes from this Wago application note: - Configuration a Profibus-DP node using Step7 and WAGO-I/O components https://www.safetycontrol.ind.br/imgs/downloads/CONFIGURATION-A-PROFIBUS-D-PDF-5973CF1775DC8.PDF It gives an example of SFC 14 (and SFC 15) with a 750-404, and shows what happens when you read the 750-04 values to MB200 (P#M200.0 in SFC 14): the value in MB200 is the Status byte, then in MB201 the LSB of the counter, until MB204 where you will find the MSB of the counter. Once the values are read in the the S7 PLC, you must read the counter value in MD 204 to have a single 32-bit result you can use in your program, and you can read/write to MB200 to see the status and send command bits to setup the counter operations.. Hope this helps, Daniel Chartier |
Last edited by: dchartier at: 02/21/2021 16:31:11 |
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2/24/2021 2:16 PM | |
Joined: 3/6/2014 Last visit: 8/20/2024 Posts: 78 Rating: (1) |
Thank for answers |
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