The aim of our project was to show the various communication possibilities between two PLC-units based on a model replicating a paintmachine and to prepare material for further education.

Available were two SIMATIC-S7 control units which were able to be linked via a MPI (Multi-Point-Interface) or Profibus-Interface.

The implementation of the software was done in STL(STatement List), a programming language similar to assembler and in SCL(Structured Control Language), a language according to the IEC 1131 standard.

The MPI-control unit communicates using a so called Global data communication. In this way, all processes which are involved in the communication together with the memoryfields to be communicated or in-and outputs were entered into the global datatable and a sender was defined for each area.. The distribution is carried out on the broadcast principle whereby the data sent can be received by more than one participant. The sending control unit does not receive any confirmation from the receiving CPL whereby this type of communication is not suitable for processes which require secure data exchange.

The communication via the Profibus is carried out either according to the Token-Passing- or the Master-Slave principal. Hereby one control unit is the master, which commands all other control-units, so called slaves, to transmit data. The data between the CPL-control units are transmitted in a cyclical manner and written the transmitting data block to the receiving data block.

The task of our dissertation was to illustrate state machines which are represented as SDL diagrams (Specification and Description Language) into a PLC (Programmable Logic Controller) of the type SIMATIC C7-626, by means of the programming language SCL (Structured Control Language). Thereby, for the state machines programmed in SCL the following demands were given:

• The SCL modules shall able to be easily adapted for any application.
• More than one same state machines shall be able to be started.
• Communication between different state machines shall be possible.

The operability of the conversion of SDL to SCL shall then be shown with a mixing plant model.

Since state machines have a status memory, we decided to use Function Blocks as modules for the SCL state machines, which get called out of the Organization Block 1 (in STL, Statement List). By clever selecting the parameters of the Function Block or the state machine, a multiple call of the Function Block (several instances) is possible without additional adjustments. In the assignment part of the Function Block the actual state machine gets out-programmed. As main part we have here a CASE assignment.

In the context of my thesis I had to examine how a cheap interface between Internet and LonWorks could be implemented. The company HEXIS, in whose co-operation this project was developed, produces peripheral power supply systems basing on fuel cells. The components of these systems communicate internally over a LonWorks network. With a gateway between the internal LonWorks network and the Internet it is possible to monitor and maintain this systems online.

Hardware: It was required that a single chip mini Web server IPC@Chip (INTEL 80186 inside, Flashdisk, costs approx. 100 DM) had to be connected with a LonWorks node to a gateway. I decided to connect them with an eight-bit parallel interface. I took ready for use hardware components for the mini Web server and for the Lon node. For the parallel interface however, the IO control signals of the IPC@Chip had to be converted by an additional hardware into the signals needed by the Lon node.

Software: In the second part of my work on the project I had to write the software for the two gateway components mini web server and Lon node.

The Gateways interface to LonWorks is formed by a number of input and output network variables defined in the program of the gateways Lon node. Throw these the gateway exchanges data with other Lon nodes.

A CGI function installed on the mini web server forms the gateways interface to the Internet. If it is started by a browser request, it transmits a dynamically created HTML page to the calling Client. Data received from the LonWorks Network is displayed on this page. Additionally the page contains dialog boxes. By pushing a button, data entered to them can be transmitted to Lon nods attached to the gateway.