EUCHNER EKS FSA with Ethernet Interface - Manual (Page 33)

Manual EKS Electronic-Key Adapter Ethernet
8 Data transfer via the Ethernet interface
8.1 Communication
This section primarily describes communication between a PC and the Electronic-Key adapter (referred to as
the device in the following).
The commands
f Program (write) Electronic-Key
f Read Electronic-Key
are transferred via TCP/IP.
Integration of the Electronic-Key adapter with Ethernet interface into the user’s PC application is supported by
an optionally available ActiveX
®
module (order no. 100 665) (usable for MS Windows
®
based programs with
ActiveX
®
capability). EKS can thus be used in conjunction with process visualization. The ActiveX
®
module is
used as a protocol driver for the TCP/IP data transfer protocols described in the following.
Euchner provides a shared library as the interface to the NCU control system of the SINUMERIK Solution Line
(Embedded Linux).
Information!
EKS is used in read-only mode in this system environment.
In order to avoid problems caused by parallel use of the TCP/IP interface and the web server, the number of
simultaneous connections is limited to one.
8.2 Basic message structure
8.2.1 IP – Internet Protocol
The internet protocol defines the basis for data transfer. It guarantees data transfer by connectionless,
unsecured transport of data packets. IP provides an addressing mechanism in order to unambiguously identify
the sender and receiver. This is done by means of IP addresses.
In addition to the actual user data that are to be transferred, a data packet also contains other important
information to facilitate problem-free data transfer. This additional information is also referred to as the packet
overhead or header.
8.2.2 TCP – Transport Control Protocol
TCP takes care of the handling and security of the IP data packets. It establishes a connection between two
network stations for the duration of data transfer. The conditions for data transfer (e.g. the size of the data
packets) are defined when the connection is set up. TCP operates according to the so-called client-server
principle. The network station that sets up a connection represents the client. The addressed network station is
known as the server.
TCP provides every data packet with a checksum and therefore ensures that any data loss is detected. A
sequence number is also transferred that calculates a so-called acknowledge number according to a fixed
algorithm. This acknowledge number is sent back to the sender. In this way, the receiver acknowledges that the
data packet has been received correctly. If this is not the case, the receiver requests the data packet again.
A further task of TCP is forwarding of data packets to the correct application. These applications (so-called
services) are addressed by means of different port numbers (e.g. port 80 for HTTP).
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