Doc: ps2001-5-1101-001 Rev: R02. 00
The software structures and organisation
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1486357009-URS, URS
| 4.1.3 The software structures and organisation (1) The software will be clearly structured and separated into the types of modules describe in summary in section 2.1; namely standard modules, application modules, template modules and document modules (the requirements for each of these are specified in §§ 4.2-4.5 respectively. (2) The Simatic Controllers require that the software is organised into discreate blocks 7 within the Controller, each software block has a logical and unique number assigned to it (the number is unique fora given type of block, blocks of different types can have the same number. It is anticipated that this numbering system shall be used as the basis of the software structure, standard modules having one range of numbers, application modules another range c however, if an alternative, beneficial and consistent structure can be envisaged, then this will be formally considered. Ladder logic or ladder diagram is one of the five permissible IEC61131-3 Ref. 008] PLC programming languages, the others being function block diagram, structured text language, instruction list and sequential function chart. In Siemens terminology, a software block is the same as a software module (and the terms are interchangeable, within the Siemens Controller there are different types of blocks, some hold software code, some are for data storage, some are used for organising the program execution and some hold code and have designated data storage area assigned to them generally a block will be used as a standard module (fora valve say, or as an application block c. Doc PS Rev R 35-71 (3) The internal structure of the software shall have distinct logical areas and order as a minimum it should have the following 1 System management and global signal generation 2 Instrumentation handling (read, scale and evaluation) 3 Safety and interlock functions 4 Continuous logic control 5 Sequence logic control 6 Command execution logic (convert continuous and sequential logic decisions to physical output signals) 7 Device handling (valves, drives c) 8 Message handling (alarms, warnings, user prompts c) 9 Communications (4) The use of subroutines for common tasks or functions (for example, string manipulation, timing functions, standard calculations, mathematical operations c) will be permitted. Where subroutines are used, these will be clearly identified as subroutine modules and will have their own area within the software structure, see § 4.1.3-(2). (5) The organisation of the software within the Controller will use the standard techniques built into the Controller and will be organised via the standard organisation blocks (OBs) available to all Controllers for cyclic processing, interrupt detection and fault handling. |