TCP/IP Special Settings

Use PLC Header

The PLC header can be used for communication with other devices where the PLC header can also be enabled.

See also PLC Header.

Life Data Acks

If you enable this option, payload frames without content are transmitted to keep a connection alive that is not used cyclically (heartbeat monitoring). Both communication partners must support this feature. For the communication with S7 PLCs, we recommend to disable this option.

Life Acks as TCP/IP Standard

By enabling this option, you can activate connection monitoring, a function that is poorly supported in many socket libraries. Life acks are frames that pass the connection status. It is recommended to enable this setting (default setting). If a WAN connection is used, you might want to disable this function for cost reasons.

Ignore TCP End Check

This setting only makes sense for Receive Direct connections.

Option enabled:

Reading in a TCP/IP frame disables its end tag. Thus, the reception buffer passes exactly the amount of data the PLC user program had requested. When data is read cyclically, this may cause problems if different data lengths were configured for the “Send Direct” and “Receive Direct” (user program) jobs.

Option disabled:

(default setting, recommended)

Excess data bytes will be ignored. This setting is only relevant to the currently edited connection (Receive Direct connection).

Life Acks with Previous Received Data

Same function as for “Life Acks as TCP/IP Standard”

If you enable this option, the data byte received last will be sent back, but with a wrong sequence number so that the other communication partner replies by sending a life ack with the correct sequence number.

Send an Ack Immediately after Received Data

It is recommended to enable this parameter if data is transmitted cyclically in a LAN. In most cases, the TCP/IP protocol collects multiple data blocks before sending an acknowledgment. If you enable this setting, the acknowledgment (ACK) is sent immediately. This increases the data rate when data blocks are sent cyclically in short intervals.

Send a Life Data Ack after the last Frame in a Sequence

This option is only available if PLC Header or RFC 1006 is used for communication.

Many socket implementations (socket libraries) do not send the IP acknowledgment frame. If you enable this function, a life data ack will be returned as an acknowledgment.

Do not Wait for Send Acknowledge

This option is only available if PLC Header or RFC 1006 is used for communication.

Option enabled:

The sending station initiates frames without waiting for the frame acknowledgment (ACK) relating to the previous frame.

Option disabled:

(default setting)

The sending station waits for the frame acknowledgment (ACK) relating to the previous frame before sending a new frame.

End Connection with FIN Instead of RST

Option enabled:

As a reply to the end connection frame (FIN), a corresponding end connection frame is sent.

Option disabled:

When a station receives an end connection frame, it resets the connection.

Use the same Port Number for both Ports

This setting sets both the source and the destination ports to the port selected in the parameterization. This disables the automatic setting of the source port to a value > 1024 in some devices (see also TCP/IP System Settings). This setting is required for the communication with CPs that do not correctly handle frame traffic via UDP.

Big Endian Format in the PLC Header

In the PLC header, the sequence number will be transmitted in the MOTOROLA format (big-endian). Usually (flag not set) the INTEL format (little-endian) is used to transmit the sequence number in the PLC header.

Change Connection Timeout

Using this setting, you can specifically change the timeout setting for connection monitoring that will end a connection when parameterizing a station remotely. This makes sense in cases where you disabled the transmission of life data acks for an Internet connection, for example. Please note that increasing this value will also increase the response time in case of connection problems (such as a broken cable).

Change Connection Memory

This setting allows you to change the memory size reserved for a connection. The minimum memory size for a connection is 1460 bytes (maximum number of payload for Ethernet connections). For a broadcast Receive connection (UDP), this setting might not be sufficient. If the partner station sends data faster than the PLC can accept it, the data will be buffered in this memory. The UDP data will only be discarded if this memory overflows.