TCP IP Modbus

[boschow]

Hello,

i have implemented TCP IP Modbus communication protocol on Freescale ColdFire micro controller. The TCP IP stack is similar to windows TCP IP stack. For the moment it has just the server part of the protocol this means that other devices can connect to it. My problem is that i don't know how to maintain the connection, because it drops after a while. I had in mind, to use interrupts, but i don't know if this is the right solution. My database has around 2000 modbus signals ... Do you guys have any solution to this problem ?

thanks and

best regards.

BoSCHoW.

[boschow]

Also when I was observing the communication with ethreal I found out this:

- the client send a TCP IP packet SYN

- then the servers responds with SYN ACK

- and then the client sends ACK

- and the client immediately sends a Modbus Query

- the server sends Modbus respond

- and then immediatly another package that is labeled TCP DUP ACK "11#1"

- and then the sequence is repeated

P.S. Sometimes the server also sends TCP Window size changed ...

I think the problem is on the server side. I don't use any functions to close the connection. I just use SocketListen, SocketRecieve and SocketSend. I also should check if the server changed the port to keep the connection active ??

Best Regards,

BoSCHoW.

Edited March 29, 2008 by boschow

[cluberti]

I would check to see if you've implemented any keep-alives, otherwise the socket is going to close without continued usage.