CP343-1 Problem for TCP connection establishment

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) or power off the whole siemens PLC system and then power on

.

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 1 192.168.0.15 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 1 192.168.0.15 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