FB_ModbusTcpClose

FB_ModbusTcpClose 1:

The FB_ModbusTcpClose function block closes a connection to a remote partner that was opened with the FB_ModbusTcpOpen function block. The number of IP connections that may be open is restricted to four, in order to maintain the use of resources at a minimum. If it is necessary to establish a further connection, a connection that is not currently in use must first be closed. A connection is automatically closed after about 10 seconds if it is not used during that period. A confirmation from the remote partner is not expected when a connection is closed. This means that under certain circumstances (e.g., if network communication has been interrupted) it can happen that a connection still exists. The remote partner should then close any such open connections. A Bus Controller operating as a remote partner closes such open connections automatically.

VAR_INPUT

VAR_INPUT
    bStart       : BOOL;
    sRemoteIPAddr: STRING(15);
    iMyPortNo    : WORD;
END_VAR

bStart: the function block is activated by a rising edge at this input.

sRemoteIPAddr: this variable is a string containing the network address (IP address) of the remote partner whose connection is to be closed.

iMyPortNo: the port number associated with the connection is passed here as a parameter. The port number is generated afresh (dynamically) each time the connection is established with the FB_ModbusTcpOpen function block.

VAR_OUTPUT

VAR_OUTPUT
    bBusy       : BOOL;
    bError      : BOOL;
    iErrorId    : WORD;
END_VAR

bBusy: if the function block is activated, this output is set. It remains set until a feedback is received.

bError: if an error should occur during the execution of the command, then this output is set, after the bBusy output has been reset.

iErrorId: supplies the command-specific error code (table) or the device-specific error code if the bError output is set.

Error Codes	Description
0x8400	Connection is already closed.
0x8401	Connection close timeout.
0x8402	Connection close resource error.

Sample of calling the function block in FBD:

PROGRAM MAIN
VAR
    fbModbusClose  : FB_ModbusTcpClose;
    bOpen          : BOOL;
    bBusy          : BOOL;
    bError         : BOOL;
    nErrId         : WORD;
    nConnectionPort: WORD;
END_VAR

FB_ModbusTcpClose 2:

In this sample, a rising edge at the bClose input causes a TCP/IP connection to the remote partner with network address '172.16.2.209' to be closed.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v2.7.0 and below	BC9xxx (165) firmware version >= 0xB6	TcModbusTCPBC.Lb6