Sunday, September 4, 2011

Communication Interface and Programming of Step 7

The communication processors are applied to ease the communication tasks of CPU. The utility of communication identifies how the stations of communication are to swap over the data and how these data are to be taken care. The function is depending on a protocol, which explains the procedure of coordination between the partners of communication. Documented utilities are functions of S7, ISO-transport, ISO on TCP Profibus, and some protocols of serial link. The functions of communication are the interface of user program to the utility of communication. The functions of communication are incorporated in the operating system of CPU and are defined by system blocks for internal communication of Simatic S7. The blocks loadable are accessible for communication with external devices systematic processors communication. Each CPU is prepared with the bus of MPI on which Siemens individual protocol is applied. The speed of transmission is up to 187.5 kb/sec and utilizes shielded two-wire fiber optic cable or copper cable, the material connector is the similar as for Profibus. The interface of Profibus can transmit data up to 12 Mb/sec through either a shielded a fiber optic conductor or two-wire copper cable. Data can be transmitted by Profibus FD, Profibus DP and Profibus FMS, also functions of S7 can be utilized.

Ethernet Industry is the subnet for link to computers. The link applies an industrial twisted pair or a double shielded coaxial cable. Also fiber optic cable is available. The interfaces of communication are ISO transport and ISO on TCP, functions S7. The speed of transmission is up to 100 Mb/sec.

The Step 7 is the software utilized for programming and configuring Simatic PLC:
•Managing projects setting up
•Parameters assigning and configuring to communications and hardware
•Symbols of managing
•S7 programmable controller creating programs
•Programmable controllers downloading programs
•Automation system testing
•Plant failures diagnosing

The Step 7 matches to the programming languages described in IEC 61131-3. The most common languages defined in IEC 61131-3 are:
•SCL (Structured Control Language) is a programming language like Pascal, which is more appropriate for creating complicated functions.
•LD (Ladder logic) is a representation graphical of the programming language. The syntax for the commands is identical to a diagram of relay ladder logic
•ST (Statement Text) is a representation textual of the programming language, identical to code of machine.
The controller of turbine is realized in FB and FC in the languages of IEC 61131-3 and the process data is swapped over Profibus by integers.


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