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S7-300 program cycle

Created by: gumis at: 5/30/2009 10:45 AM (12 Replies)

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5/30/2009 10:45 AM	Rate (0)
gumis Posts: 45 Rating: (0)	Dear all, I have connected CPU314 with CPU315-2DP via MPI cable. I am using SFC15 in CPU315-2DP to data transmission. When the CPU315-2DP will read the data from memory space of CPU314? When the CPU315-2DP will write these data to its specified memory space? I mean, does the execution of SFC15 depends on their location in OB1 or maybe is it executed before of after the OB1 execution?
gumis Posts: 45 Rating: (0)
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5/30/2009 2:20 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 12/9/2025 Posts: 2957 Rating: (243)	Hi, I can't tell you really how this function works in detail, but the fact is that you read data on other CPU only with function SFC14 (if you write with SFC15), you its not important for you when you really get data, but important when you read it. So after calling SFC14 you should check an error code and if there is no error then you can use memory which contains transfered data.
	Best regards, Darius
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5/30/2009 3:16 PM	Rate (0)
gumis Posts: 45 Rating: (0)	Thank you. I meant SFC67 instead of SFC15 in the first post but now I understood what I wanted.
gumis Posts: 45 Rating: (0)
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5/30/2009 5:38 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 12/9/2025 Posts: 2957 Rating: (243)	Hi, Its equal. Still you'll get valid data after communication function returns you no errors. I just can't say exatly when your real data transfer occurs: immediately after function call or at scan cycle start. In any way communication read function gets data on it's call. So no matter when real data transfer occur you can think that you data read/write is function call. Maybe other forum members will correct me, but in general this is true.
	Last edited by: Darius at: 5/30/2009 5:38 PM Best regards, Darius
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This contribution was helpful to 1 thankful Users gumis

5/30/2009 7:50 PM	Rate (0)
Ayman Elotaify Diamond Member Joined: 5/28/2008 Last visit: 12/29/2025 Posts: 4522 Rating: (843)	Dear gumis, If data you want to transfer between the two CPUs are less than or equal 22 bytes, then the best and the simplest solution is to use global data communication. Just what you have to do is to open the net pro and define a table of global data. Regards, Attachment GD.zip (410 Downloads)
	Ayman Elotaify
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This contribution was helpful to 1 thankful Users gumis

6/1/2009 10:25 AM	Rate (0)
gumis Posts: 45 Rating: (0)	The reason I am asking is like the following, X_GET function used in CPU315-2DP reads state of digital inputs (I0.0-I0.7) in CPU314. The CPU315-2DP writes these values toits digitaloutputs (Q0.0 -Q0.7).These PLCs communicate in MPI network. I have measured delays between appearance of logic '1' on specific input of CPU315-2DP and appearance of logic '1' on its corresponding digital output of CPU314. I have examined two rates of transmission speed (187.5 and 19.2kbit/s). I have done ten tests for each speed. Before measurements I have expected that differences between received values of delays will be the same. But for 19.2 values of delays differ from 122ms to 254ms. For 187.5 the values differ from 40 to 61 ms. I hope it sounds clearly. Best regards, gumis
gumis Posts: 45 Rating: (0)
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6/1/2009 11:28 AM	Rate (0)
Ayman Elotaify Diamond Member Joined: 5/28/2008 Last visit: 12/29/2025 Posts: 4522 Rating: (843)	gumis The reason I am asking is like the following, X_GET function used in CPU315-2DP reads state of digital inputs (I0.0-I0.7) in CPU314. The CPU315-2DP writes these values toits digitaloutputs (Q0.0 -Q0.7).These PLCs communicate in MPI network. gumis Mr. gumis, I am still sure that global data communication method is the easiest method for you in your application. As I told you before, you can transfer data from CPU to the other CPU linked on the same MPI network. Just what you have to do is to write the source address (in your example IB 0) in the column of CPU 315-2DP. and write also the destination (in your example QB 0) in the column of CPU 314. Ten define the sender CPU for this row as mentioned in the attached picture. gumis I have measured delays between appearance of logic '1' on specific input of CPU315-2DP and appearance of logic '1' on its corresponding digital output of CPU314. I have examined two rates of transmission speed (187.5 and 19.2kbit/s). I have done ten tests for each speed. Before measurements I have expected that differences between received values of delays will be the same. But for 19.2 values of delays differ from 122ms to 254ms. For 187.5 the values differ from 40 to 61 ms. gumis Actually, I do not know how did you mesure it. But remember that we are talking here about MPI network. It covere up to 187.5 kbps.Of corse If you used global data method the delay will decrease, as the CPU now will not cunsume time in program. Each CPU have something called bit instruction time and word instruction time which represents how many micro-seconds the CPU need to execute that instruction. So In X_Get functions that time is more than that in GD communication. But the difference will not toobig or in other words, it won't be considerable. But let me know If your application can not work with that small delay? Regards, Attachment gd1.JPG (394 Downloads)
	Ayman Elotaify
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This contribution was helpful to 1 thankful Users gumis

6/1/2009 11:46 AM	Rate (0)
gumis Posts: 45 Rating: (0)	Dear Mr. Ayman Elotaify My application can work with such delays but I am student and my purpose is to learn as much as possible. I will use GD communication but it will not resolve my problem.
gumis Posts: 45 Rating: (0)
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6/3/2009 2:50 PM	Rate (0)
May Posts: 24 Rating: (0)	Sir, GD communication is suppose to be simplest. In my application I tried for 400 and 300 cpu. I was not bothered about delays it occurred. thanks
May Posts: 24 Rating: (0)
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6/4/2009 1:17 PM	Rate (0)
Ayman Elotaify Diamond Member Joined: 5/28/2008 Last visit: 12/29/2025 Posts: 4522 Rating: (843)	Hello May, You can use GD communication with both S7-400 & / or S7-300 together without problems.Thus becauseyou can integrate the two software of S7-400 & S7-300 into one project and go toNet-Pro and insert your tables for GD-communication. Regards,
	Ayman Elotaify
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