connect mitsubishi PLC Ethernet card with RSView 32


Thread Starter

rakesh kadian

can any one help us in making a reliable connection between a mitsubishi plc ethernet card communication with RS View 32 via melsec opc
software what preciously i need a solution for no breaking of connection in between as this communication is working well but not relable as it goes down in between & so we had putted error handler for that in program of mitsubishi plc to handle this.

Mark Hensley

Dear Rakesh,

I have seen similar issues when I developed our driver for the Mitsubishi Ethernet interface. It required me to write some ladder logic for the PLC
to handle error conditions. It works most of the time but I have seen conditions occur where the PLC needed to be cycled before it would accepts a
new TCP/IP connection. The error seems to occur if there is a true physical break in communications or loss due to excessive noise. When this occurs the PLC can not receive a proper shut down of the TCP/IP connection. This causes the PLC to hold the last connection open thus not allowing a new connection to be established. In the Mitsubishi PLC the Ethernet interface will accept up to 8 connections but it does so using 8 unique port addresses. This means that it can truly only accept 1 connection on a given port. If the connection for a given port is considered to be in use from the PLCs standpoint, any attempt to connect to that port will be rejected.
This is what occurs when you temporarily lose communication with the PLC. The PC running the Melsec OPC server( Vendor ?) sees a communications
failure, it eventually will close its current TCP/IP session. If the PLC does not see this close request the PLC will consider the connection to still be active. Once the Melsec OPC server closes its connection it will attempt to reopen the connection but it can't because the PLC still sees it as an active connection on that port.

This is where the PLC ladder logic is suppose to come to the rescue, unfortunately from my own experience I have seen conditions where the status
bits for a given connection do not give you any indication that there is a problem. Without some form of feedback in terms of status bits you have no way of knowing when you should force the PLC to drop the current connection and wait for a new one to established. The code that we show in our help file tries to do that but like I said sometimes the status bits don't seem to get set such that the code can execute.

If you're curious try downloading our server using the web install. When the install runs select only the Mitsubishi Ethernet driver. That way you will get the Mitsubishi help file that contains the Ladder Logic we use. Once the install is complete simply copy the help file out to a new directory and run the web install again to remove the server. That way you get the help file without the bulk of the program remaining on your PC.

Mark Hensley
Kepware Technologies
81 Bridge St.
Yarmouth Maine 04096
PH: 207-846-5881 ext. 202
Fax: 207-846-5947
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