Establishing communication, internal data point

The TCP/IP protocol is used for the connection to the SK-1703 remote head of the SAT system, with BSD 4.3 sockets used as the interface. The SK-1703 station needs the following devices for the TCP/IP connection:

  • an SK-KE/ET system element with
KR-GPU2 hardware module on which the Application Software Layers run,
a KR-ET Ethernet interface with standard D-15 MAU KE/ET firmware

  • 10BASE2 or 10BASE5 Ethernet transceiver
The following TCP/IP parameters must be configured in the KE/ET:
Length Parameter
4 bytes Own Internet address
4 bytes Addresses for each remote host
2 bytes TCP/IP port number (default 2073 - should not be changed)
4 bytes Internet address of the gateway, if necessary (default: not defined)
4 bytes Subnet mask (default: not defined)
On the WinCC OA side the following parameters are required to establish a connection successfully:

  • Internet address of the destination station(s)

  • Optional host name(s) of the destination station(s) in /etc/hosts

  • TCP/IP port number(s) in the configuration file - please refer to the Configuration file section.

  • An entry in the configuration file for each connection - please refer to the Configuration file section.
At system start-up the connections should be established sequentially to avoid overloading the system. A general query is issued automatically by the SK 1703 after establishing a connection.
Hotlinks (commands) are ignored until the driver is ready for communication.
For each pre-stored system component the SSI driver provides an Alive mechanism for line monitoring purposes; an Alive data point of type _SSI_Alive can be created for each driver.

data point _SSI_Alive_1

Sheet Data type
AliveSndDp natural number
AliveSndTimeOut natural number
AliveRcvDp natural number
AliveRcv2Dp natural number
AliveRcvTimeOut natural number
ActivateDataTypes bit
WhichDataTypes bit pattern
This data point must have the name _SSI_Alive_<num>, where <num> specifies the driver number. The Alive monitoring between KE/ET and driver is performed using pulse commands. The AliveSndDp element of this data point of type natural number can be given a peripheral address. A send Timeout (element AliveSndTimeOut) then specifies the time intervals at which this Alive data point is to be sent by the driver. This data point is sent cyclically by the driver itself without the Event Manager being informed, which is why the sending of this data point may not be displayed.
There is an equivalent mechanism in the receive direction to check whether messages are received from the pre-stored component within a configurable period (implemented by the AliveRcvDp and AliveRcvTimeOut elements of the Alive data point). The AliveRcvDp should have a filter config (e.g. old-new comparison or time-dependent filtering, in case the received value changes every time), otherwise it is sent to the Event Manager every time the message is received. If the Timeout has elapsed without a message being received from the component, this component is set to invalid until another message is received from it.
After a temporarily broken connection is restored, the KE/ET automatically issues a general query and sends the data to the host.
The Alive data point also provides the driver with two elements for blocking commands: the ActivateDateTypes data point sheet (of type bit) blocks outgoing commands from the driver (if set to "1"); the WhichDateTypes data point sheet (of type bit pattern) provides an additional filter mechanism for outgoing commands (if ActivateDataTypes is set to "1"). This sheet contains data type bits (0 to 31); commands are only sent if their data types are set in this sheet. If ActivateDataTypes is set to "0" then all commands are sent and WhichDataTypes is then irrelevant.