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Ethernet communication timing

Created by: h2_504 at: 9/15/2014 3:49 PM (8 Replies)

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9/15/2014 3:49 PM	Rate (0)
h2_504 Experienced Member Joined: 11/8/2011 Last visit: 3/18/2025 Posts: 92 Rating: (1)	Dear all, When does the Ethernet communication happens? At the end of scan cycle or it can happen during scan cycle? h2_504

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9/15/2014 4:04 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello, do you use a PN-CPU or a CP? Do you want to know when data are transferred to the user program or when they are sent on the line? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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9/15/2014 5:02 PM	Rate (0)
h2_504 Experienced Member Joined: 11/8/2011 Last visit: 3/18/2025 Posts: 92 Rating: (1)	Hi! I am using a CPU with PN interface but the question remains for CPs. Also what is interesting to find out is how the communication in both directions works, although know my interest is only on the data read by a SCADA from the CPU. Best regards, h2_504

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9/15/2014 5:17 PM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello, the CPU and the CP run asynchronously. Data transfer from the CPU to the CP and vice versa is carried out when AG_SEND / AG_RECV is called in the CPU. The CP has got a task list internally which is carried out cyclically. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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9/16/2014 9:50 AM	Rate (0)
h2_504 Experienced Member Joined: 11/8/2011 Last visit: 3/18/2025 Posts: 92 Rating: (1)	Hi! But what about the CPU with PN interface. When does the CPU communicate with a SCADA? I am asking that because inthe CPU there is no part of the code wich hadles the communication. The SCADA is reading/writing to a DB. When does this happen with respect to scan cycle? At the end or during scan time? h2_504

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9/16/2014 11:18 AM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello, there is of course code executed to transfer send and receive data from the main CPU program to the TCP stack of the CPU. TSEND and TRECV are required for this with TCP native communication. When you use PUT and GET communication, the passive part of them is carried out at the cycle check point. The active part need a FB call as well. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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9/18/2014 10:15 AM	Rate (0)
h2_504 Experienced Member Joined: 11/8/2011 Last visit: 3/18/2025 Posts: 92 Rating: (1)	Dear Kaulquappe, What I am trying to understand is when a PC with WinCC takes data from a DB. To do this type of communication the PLC software doesn't need to include any function. So the question is when does the Ethernet interface takes data from the DB to send it to the PC: at the end of the scan cycle or during the scan cycle? h2_504

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9/18/2014 10:56 AM	Rate (0)
Kaulquappe Posts: 3093 Rating: (324)	Hello, I'm sorry, I'm not experienced with WinCC. Probably somebody else can help. Just a hint when you start your next thread in the forum: describe more exactly what your configuration is about and which information is important for you. Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (324)
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12/15/2014 9:46 AM	Rate (0)
Gärchla Posts: 457 Rating: (46)	Hello, connection of PLC to HMI (WinCC) through a Ethernet channel is like a "black box". Values of DB defined in PLC and connected via "HMI_connection_1" in WinCC will be transmitted withoutuser defined actions. To get a more detailed view on Ethernet communication we must know type of PLC. Years ago, I have developed a program for communication to a PBXlike FTP. You open a channel,send a request, check amount of bits, receive (transmit) data bit by bit, get EOF-mark, close channel. That is the rough rule for Ethernet communication. So,to your question abouttime trigger: when does PLC sends data from DB? To make more detailed statements, we have to know type of PLC and then I have to check communication in system manual. For a S7-1200 (for example) please find system manual here: https://support.automation.siemens.com/WW/llisapi.dll?query=39710145&func=cslib.cssearch&content=adsearch%2Fadsearch.aspx&lang=en&siteid=cseus&objaction=cssearch&searchinprim=0&nodeid0=4000024&redir=false&x=0&y=0 Chapter 7 decribes communication between PLCs, 7.5 is dealing with Ethernet. Please check this. Chapter 7.8 informs about S7-communication, I think this will be the interesting point for you. On the other side, I could not find anything about triggers: I think this is the very secret of S7-systems. Personally, I have no experience in S7-"core"-programming and therefore I would suggest to check manual mentioned above. What is your thought regarding in-depth-programming of connection? Does connection not work, is there a hardware failure? Regards Georg
Gärchla Posts: 457 Rating: (46)	Last edited by: Min_Moderator at: 12/15/2014 4:43 PM
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