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[SOLVED] Can't get TRCV_C to work (S71212C <-> pc application (tcp sockets))

Created by: FerMC at: 6/9/2010 5:45 PM (3 Replies)

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6/9/2010 5:45 PM	Rate (0)
FerMC Posts: 2 Rating: (0)	Good morning: I'm trying to estabish a tcp communication between the S71212C PLC and a pc application. I have setup the PLC as tcp server and the pc application as client. The goal is to replace an existing RS232 connection between another PLC and a PC program. I have tested the client application using the loopback interface and a server application, and both sending and receiving work. Both applications (PCL and pc) are stripped down and only handle the communication. So far I have been able to send strings from the PLC to the client application and receive them. Nevertheless receiving on the PLC strings that have been sent from the client application, has been impossible until now. (Yes, once more receiving seems to be more difficult than sending ) I have used both the TCON, TRCV, TSEND combo and just TRCV_C and TSEND_C. The result is the same: the PLC send, but won't receive. TRCV_C: CONT=1 so that the connection is always opened. EN_R = 1 then BUSY=1 STATUS:7002 (reception not finished yet) or TRCV_C: CONT=1 so that the connection is always opened. EN_R = 0 then BUSY=0 STATUS:7004 (Connection established. Not doing anything) I'm about to buy a RS232 communication module (back to the past ) Has anybody any tips or ideas as to what might be happening? Thanks in advance. Regards, Fernando
FerMC Posts: 2 Rating: (0)	Last edited by: FerMC at: 6/10/2010 1:48 PM
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6/9/2010 8:34 PM	Rate (0)
Darius Platinum Member Joined: 9/28/2005 Last visit: 3/15/2025 Posts: 2957 Rating: (243)	Hello, I have successfuly completed the same task as you. Its very hard to determine your problem because I can't see your PLC side of the program and I can't see what you did with PC ? What software on the PC communicates with the PLC ? I can tell you that PLC side was exactly the same as here for me. I wrote program with C# .NET on PC side for communication with the PLC. There was no examples for that. I just used Open TCP comunnication, no SIMATIC.NET, no OPC servers, just Open TCP. If you like to use PC Access on PC side, you can look here.
	Best regards, Darius
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6/9/2010 8:47 PM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	Hello, Most of the problems reside in the parameter "LEN". If you set it for instance to 1000, than you will only get data in the PLC if the buffer has effectively be filled up to byte 1000. If the PC sends one hundred bytes, you will need ten messages before you get 1000 bytes in the PLC. Pay attention that by default LEN=0 The default setting of the LEN parameter (LEN = 0) uses the DATA parameter to determine the length of the data being received.
	Last edited by: jklm at: 6/9/2010 8:55 PM Best regards jklm Suggestion was helpful? Feel free to rate it.
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6/10/2010 1:54 PM	Rate (0)
FerMC Posts: 2 Rating: (0)	Thank you both for your answers. Darius I have successfuly completed the same task as you. [...] I wrote program with C# .NET on PC side for communication with the PLC. It was encouraging, that you had done the same thing. I am using VB.NET (so more or less the same because of the CLR) on windows and plain c++ on linux. Darius Most of the problems reside in the parameter "LEN". Pay attention that by default LEN=0 The default setting of the LEN parameter (LEN = 0) uses the DATA parameter to determine the length of the data being received. That was my mistake.In the TRCV_C block LEN was set to 0 and my Data parameter was a string with a maximum lenght of 12 characters. I didn't initialize this string, so the actual lenght of it was 0. I assumed that it would work because the TSEND_C block was working with LEN=0, but there the string was initialized. Setting LEN to the lenght of the string in the TRCV_C block resolved the issue. Regards, Fernando
FerMC Posts: 2 Rating: (0)	Last edited by: FerMC at: 6/10/2010 2:04 PM Last edited by: FerMC at: 6/10/2010 1:54 PM
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