Doc: ps2001-5-1101-001 Rev: R02. 00
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1486357009-URS, URS
| Block types and usage (1) All block types available to the Simatic Controller may be used in the production of the software, these are 1 Organisation block (OB) Interrupt driven block called in response to a specific event detected by the Controller operating system 2 Function (FC) A subroutine (with or without parameters) used to structure the software or handle recurring or complex functions 3 Function block (FB) Similar to an FC but with an allocated retentive data area (an instance data block) 4 Data block (DB) Free format storage areas used to hold any form of user data 5 Instance Data block (iDB) Retentive data area assigned specifically to a function block 6 User Data Type (UDT) A user defined data structure (technically, not a block but widely used within data blocks) (2) While all the above blocks are available and may be used as required, it shall be preferred if functions (FCs) are used in preference to function blocks (FBs) wherever possible, these being easier to understand and use. Separate justification need not besought by the developer for the use of function blocks, function blocks should be used where their facilities are necessary however, function blocks should not be used if a function (FC) can achieve the same requirements. Doc PS Rev R 37-71 (3) The Simatic Controllers and the TIA Portal programming environment have builtin system blocks that perform specific functions (for example, a PID 8 control loop, these blocks will be used wherever possible in preference to developing anew block with similar functionality. 4.2 Standard module requirements (1) The standard modules will form the basis of the library of software modules, there will be many such modules with each performing a different function (for example, a block to control an isolating valve, a block to read and scale an instrument, a block fora PID controller c, see ยง 4.2.2 for more information) (2) Each standard module will be either complete and self-contained (i.e. does not require any other software module to perform its function, with the exception of those system modules that create common global signals, or will be part of a family of modules (for example, a communication send module that transmits data, could have a partner re- ceive module to receive the data. (3) It may be that some complex processes require the use of more than one block to achieve a purpose for example, controlling and managing a sequential process may require an overall management block that controls the progression of the sequence as a whole and may also have a step block that handles the actions and transitions for each step and is called multiple times within the sequence. This type of module arrangement will be permitted. (4) Where multiple standard modules are used to achieve a purpose, as explained in Download 1.5 Mb. Share with your friends:
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