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Modbus TCP communication problem between Schneider PLC and S7-300 with CP343-1

Created by: RichardG at: 7/20/2009 8:44 AM (5 Replies)

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7/20/2009 8:44 AM	Rate (0)
RichardG Posts: 4 Rating: (0)	Hi All! I have a strange problem with Modbus/TCP communication between Schneider Pentium CPU 651 and S7-315-2DP with CP343-1. The CPU is S7-315-2DP with CP343-1, The PLC acts as client and Pentium CPU 651 as a server. According to the detail description of manual, I set up the communication and at the beginning the communication seems OK( The data could be send to/received from Schneider side). The problem is that the communication is interrupted sometimes and could not be recovered again). In order to solve this problem, I make a testing as following: 1. when the communication is OK, I plugged out the ethernet cable for 60s(normally above 1 minute). 2. Monitor the CP343-1 status via web navagator, from TCP options, TCP connections Number Local IP address Partner IP address Local port Partner port Status 3 192.168.0.14 1 92.168.0.15 2000 502 SYN_SENT The status is always SYN_SENT, and I can find the LED for Tx(ON CP343-1) flashed once every about 4 seconds. and then the communicaiton could not be established again. 3. Run ModSim32 on My laptop to simulate the server with same IP address and start communication, normally in 10s the CP343-1 could establish connection with ModSim32(On my laptop). 4. Monitor the CP343-1 status via web navagator, from TCP options, TCP connections Local IP address Partner IP address Local port Partner port Status 192.168.0.14 1 92.168.0.15 2000 502 ESTABLISHED 5. then I remove the ethernet cable from my laptop and connect it to Schneider PLC in 10s. in most time, the communication works well again. It is really a big problem, It seems the communication is not stable, sometimes it lost connection, the client could not accept it. Does anyone has any suggestions? Thanks a lot in advance! Richard
RichardG Posts: 4 Rating: (0)
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7/20/2009 8:55 AM	Rate (0)
Kaulquappe Posts: 3093 Rating: (323)	Hello Richard, do you get the ERROR-Bit and an error number in STATUS at FB Modbus? Regards, Kaulquappe
Kaulquappe Posts: 3093 Rating: (323)
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7/20/2009 9:02 AM	Rate (0)
RichardG Posts: 4 Rating: (0)	Hi,Kaulquappe When status of TCP connection is in "SYN_SENT", I get ERROR-BIT=1 and FB STATUS=8183H when status of TCP connection is in "ESTABLISHED", the ERROR-BIT=0. Thanks a lot and best regards! Richard
RichardG Posts: 4 Rating: (0)
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7/20/2009 10:13 AM	Rate (0)
YngSoul Posts: 15 Rating: (1)	Hi RichadG, It could be that the Schneider CPU doesn't recognise that the communication was interrupted and when the client send a new request, the Schenider doesn't answer coz, for it the connection is allready established. I think you should restart the Server CPU after an interrupted connection. Good luck! YngSoul
YngSoul Posts: 15 Rating: (1)
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7/20/2009 1:22 PM	Rate (0)
RichardG Posts: 4 Rating: (0)	hi, Everyone: Now I found same problem occurs whenS7-315-2DP with CP343-1 lost power and power on again. when siemens system power on again. It is very difficult to get connection with Schneider system. Does anyone has good idea or experience? Regards! RichardG
RichardG Posts: 4 Rating: (0)
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7/20/2009 8:02 PM	Rate (0)
jklm Platinum Member Joined: 12/22/2006 Last visit: 1/25/2022 Posts: 1742 Rating: (309)	hello, From all previous messages, i come to the conclusion that the problem is not at the Siemens PLC side, but more at the Schneider side. In my opinion, the following is happening: - after a connection loss (for instance after power down of the Siemens PLC), the PLC sends a SYNC message to the Schneider system (this is the requestfor a new connection) - but the schneider CPU considers that the prevouis connection is still active and does not accept the new connect request. - untill the connection keep alive timeoutis reached at the Scnieder side. To be very sure of that, you could take a trace of the traffic on the wire by using "wireshark" on a PC used as monitoring system + a hub (or a switch with port monitoring capability like scalance X200). Wireshark is a freware (see www.wireshark.org) Look if you can reduce that timeout at the schneider side to accelerate the acception of a new connection.
	Best regards jklm Suggestion was helpful? Feel free to rate it.
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