Saturday, September 3, 2011

Hardware and Operating Software of Siemens S7 PLC





The automation system of Simatic is a coordinated components range. The key unit comprises a CPU and a memory to save the user program. The key unit performs communication with other modules that are linked through the bus of MPI (multi-point bus). The bus of MPI is applied to set up a subnet in which user interfaces of CPU and devices of programming can swap over the data. There are a lot of different modules that can be connected. The mainly important for this work is the CP (communication processor) that attaches the PLC to various networks.

There are CPs for Industrial Ethernet, PROFIBUS, FMS, and others. The CP of Industrial Ethernet can be utilized to set up the connections of ISO on TCP and ISO Transport. The Simatic key units come prepared with diverse hardware for different commands on the capabilities of processing. The family of Simatic S7 contains of some modules that are installed on a rail. For a whole unit of a CPU unit and a power supply is required. The units of CPU have different memory quantity and capabilities of performance to ensemble different user’s requirements. The modules of I/O can be applied to enlarge the capabilities systems to control the tasks, even though the more I/O, the more memory and performance it acquires to process them. The controller of turbine utilizes both distributed I/O and hardwired I/O over Profibus.

The environment of software
The complete program of a CPU consists of the operating system and the user program.

System Operation
The system operation includes declarations and instructions of internal functions of tool operation and is proprietary to Siemens. There are some SFB (System Data Blocks) and SFC (System Functions Ready) to apply in the system operation. The System Functions Ready are functions with no a memory and its parameters must be processed by the user program right away, whereas the SFB has a memory and its output can be admittance anytime and anywhere in the operator program.

User program
It contains all programmed declarations and instructions to control the task. The user program is generally separated into a functional unit or self-contained technological. These units are defined as blocks. The FB and FC operates the same method as SFB and SFC, but they are not an element of the system operation they are programmed by the user program. The organization block is an element of the user program and are defined and processed by the system operation when firm events happen. The priority of organization blocks tagging manages the actions taken by the CPU on events.


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