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TLS_SEND

Note
For this function block, a new implementation is available which requires firmware version 2021.3 or newer. The new FB combines the handling of TCP and TLS communication. Furthermore, it supports that one TCP/TLS server can communicate with several clients. Refer to the topic "TLS_SEND_2" for details.

Type Function block
DescriptionThe function block is used to send data via TLS (Transport Layer Security) to a TLS-capable Ethernet device. This is done using a TLS socket. The TLS socket must first be opened using the TLS_SOCKET function block before data can be sent.

Once the socket is opened and a connection is established, the function block sends data to the communication partner either via a pure TCP connection or a TLS-secured connection. The type of connection used depends on the value of the START_TLS input of the TLS_SOCKET function block:

  • With START_TLS = FALSE, the function block uses a pure TCP connection to send data.
  • With START_TLS = TRUE, the function block sends data via a TLS-secured connection.
The function block provides a security check for identifying whether the IEC application expects the data to be sent unsecure (via a TCP connection) or secure (via TLS-secured connection). The security check is done by comparing the values of the SEND_SECURE input of the function block and the START_TLS input of the TLS_SOCKET FB. If an inconsistency of the input values is detected, for example, SEND_SECURE = TRUE (IEC application requires secure transmission of data) and START_TLS = FALSE (TLS protocol not yet initialized), the ERROR output is set to TRUE and the error code 16#C150 is indicated at the STATUS output.

Each transmission operation is triggered by a rising edge at the request REQ input. During this cycle, the function block copies the data to be sent (applied to the DATA input) into an internal buffer. The BUSY output is set to TRUE as long as data are being sent from the internal buffer. While BUSY = TRUE, the REQ input is ignored. The transmission of new data that are available at the DATA input during the ongoing transmission cycle can only be triggered with a rising edge at the REQ input once the BUSY output has been set to FALSE.

If the connection is broken and the communication partner cannot be reached, the ERROR output is set to TRUE for one cycle. The corresponding error code is provided at the STATUS output within this cycle.

WARNING
Unintended machine operation
Verify that the influence of the output data cannot result in an unintended or hazardous behavior of the entire system.

Notes
  • The TLS socket opened by the TLS_SOCKET function block can only be used for subsequent calls of the TLS_SEND function block as long as the ACTIVE output of the TLS_SOCKET function block is TRUE. Calling the TLS_SEND function block while ACTIVE = FALSE causes an error at the TLS_SEND function block (ERROR = TRUE and STATUS code = 0xC210 issued).
  • The TLS socket handle created by the TLS_SOCKET function block is not compatible with the TCP socket handle created by the TCP_SOCKET function block. The TLS socket handle can only be used with the TLS_SEND/TLS_RECEIVE function blocks and the TCP socket only with the TCP_SEND/TCP_RECEIVE function blocks.
  • For controllers with integrated firewall, make sure that the firewall does not block the ports involved in the communication. Otherwise, the connection cannot be established.
  • Function blocks have to be instantiated.
    The instance name of the function block has to be declared in the 'Variables' table of the POU where the FB is going to be used. The instance name must be unique within the POU.
ParametersInputs

REQ

HANDLE

DATA_CNT

SEND_SECURE

Input/Output

DATA

Outputs

DONE

BUSY

ERROR

STATUS