FAQ on SIMATIC. Programming a State Machine in Programming Language STL FAQ

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Kristin Boyd
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1 FAQ on SIMATIC Programming a State Machine in Programming Language STL FAQ

2 Table of Contents Table of Contents... 2 Question... 2 How can I create a state machine for SIMATIC in programming language STL?... 2 Answer... 2 The instructions and notes listed in this document provide a detailed answer to this question The State Machine Setup of a state machine Advantages of the state machine Disadvantages of the state machine Programming a State Machine in STL Basic structure of the program Realizing a state machine in STL Evaluating the start conditions (network 1) Jump distributor (network 2) States of the state machine (networks 3-22) Summary Processing of the block by the program Expansion of the block example by further states History... 9 This article is taken from the Internet offer of Siemens AG, Automation and Drives, Service & Support. The following link takes you directly to the download page of this document. Question Answer How can I create a state machine for SIMATIC in programming language STL? The instructions and notes listed in this document provide a detailed answer to this question. V /9

3 1 The State Machine 1.1 Setup of a state machine A state machine consists of various states, which have various switching conditions and a start condition for starting the state machine. The following state machine shall be illustrated as an example: Figure 1-1 Structure of a state machine States 1 to 3 each perform specific functions which are programmed within the states. The state machine is set to state 1 via the input signal Execute=True using the start condition. State 0 "Error" can be jumped at from any state of the state machine. The machine then remains in this state until the switching conditions leads the state machine back to state 1 via the Execute=True signal. In state 1 the switching conditions can be set so that the state machine either branches to state 2 or state Advantages of the state machine The state machine offers the following advantages: Only the program code of the state machine currently programmed in the current state of the state machine is active. A mutual impact of the program code is not possible. The transitions between the individual states are clearly defined. This prevents faulty transitions into other states. Programming of the state machine can be structured clearly and simply in an STL block. Changes in the program code only affect the state of the state machine in which they are programmed. V /9

4 1.3 Disadvantages of the state machine The state machine has the following disadvantages: The execution of the program code may be slightly slower than when programming the same function with step chains. 2 Programming a State Machine in STL 2.1 Basic structure of the program The basic structure of the STL block for programming a state machine is divided into the following sections: Figure 2-1 Basic structure of the program STL Block of the State Machine Evaluating the start conditions of the state machine Jump distributor for the individual states of the state machine Error state Error treatment within the state machine State 1 Program code of state 1 of the state machine State n Program code of state n of the state machine State Ready End state of the state machine without further branching 2.2 Realizing a state machine in STL The references to the networks of the STL block refer to the STEP 7 archive attached to the FAQ and the STL blocks contained in it Evaluating the start conditions (network 1) In network 1 the boolean input variable Execute of the block is evaluated. If a rising edge is recognized at this variable (False True) the program code is executed in this network. V /9

Figure 2-2 Network 1 Evaluating the start conditions For the start of the state machine the Sequencer variable, which represents the currently active state of the state machine, is loaded with the

5 Figure 2-2 Network 1 Evaluating the start conditions For the start of the state machine the Sequencer variable, which represents the currently active state of the state machine, is loaded with the value 1 (for state 1). Additionally the variables for the switching conditions are reset in the individual states Jump distributor (network 2) The jump distributor forms the core element of the state machine. Figure 2-3 Network 2 Jump distributor In the jump distributor the dependency of the Sequencer variable is branched into the individual states of the state machine. V /9

6 The jump distributor, together with the basic program technology setup of the individual states, ensures that only the program code for the currently active state is active in the program. In the jump distributor principally all states of the state machine are generated with their jump labels, so that they can be jumped at by setting the Sequencer variable. Variable sequencer exceeding the range Should the Sequencer variable take on a value larger than the jump table, it is branched to the error state at jump label SQEr of the jump table. In this exemplary case the CPU is brought to operating state "Stop" via system function SFC 46 "STP" States of the state machine (networks 3-22) The individual states of the state machine are principally made up of four networks. Start of state jump target The jump target of the jump distributor and hence the beginning of the state is programmed in an own network for clarity reasons. Figure 2-4 Jump target Program code of the state The program code to be executed within this state is programmed in the next network. Figure 2-5 Program code of the state In this network you can insert the program code required for this state. The program code can of course also be divided in several successive networks within the state. Switching condition As the last but one network of the state the evaluation of the switching condition follows. V /9

7 Figure 2-6 Switching condition When OK_Step01_02 is set, then change to subsequent state 2 When OK_Step01_03 is set, then change to subsequent state 3 Here the Sequencer variable of the state machine is assigned with the number of the subsequent state dependent on the variable set in the program code of the state (e.g. OK_Step01_02 or OK_Step01_03). As shown in the figure, several branching options can also be programmed simply and standardized End of the state Jump to the end of the state machine At the respective end of the state it is important in the program to jump to the end of the state machine with an absolute jump in order to leave other states of the state machine unprocessed. Figure 2-7 End of the state The end of the state machine is mostly formed by the last network of the block. Figure 2-8 End of the state machine or the block This ensures that within the state machine only the currently active state is processed which has currently been selected via the jump distributor in network 2 using the Sequencer variable. V /9

8 3 Summary 3.1 Processing of the block by the program As a summary, the processing of the STL block of the state machine by the program shall be represented in a graphical display. Figure 3-1 Processing of the state machine by the program Start of the block When starting the block via Execute=True, the start condition is processed once and the state machine set to state 1. State 2 active Switching between the individual states only occurs via the Sequencer variable which branches into another state using the jump distributor. Error scenario In case of an error the Sequencer variable can be set to value 0. The state machine then branches into state 0 Error and remains in this state until the state machine is restarted via the Execute variable. Note Before branching into state 0 Error the number of the current state of the Sequencer variable should, if possible, be saved into a further variable before the sequencer is overwritten with the value 0. This procedure may facilitate error diagnostics in case of an error. V /9

9 3.2 Expansion of the block example by further states For expanding the example block contained in the STEP 7 archive by further states, you proceed as follows: Table 3-1 Presetting of the superimposed synchronism conditions of the axes No. Instruction Note 1 Copy networks 7 to 10 of state 1 as a template to the end of the block before network 23. Copy the blocks in the number of states you wish to expand the state machine by. 2 Adjust the jump labels at the beginning of the inserted states (SQxx) to the number of the new state. 3 In the title bar of the networks you adjust the number of the newly inserted state (Step xx). 4 Adjust the jump labels in the switching conditions (SxxE) to the number of the new state. 5 In the switching conditions you adjust the values for the subsequent states (those loaded into the Sequencer). 6 Integrate the jump labels at the beginning of the newly inserted states into the jump distributor in network 2. 7 Supplement network 1 by possibly necessary initialization processes for the newly added states. Ensure during copying that the end of the state machine (jump label SQEd) always stays behind the inserted networks. Please consider the labeling of the jump labels for several branching options. 4 History The state machine is now already functioning and can be loaded into the controller. Subsequently, the program code of the individual states of the state machine can be developed. Table 4-1 History Version Date Modifications V First issue V /9

Training document for the company-wide automation solution Totally Integrated Automation (T I A) MODULE C1 Sequencer programming with S7-GRAPH

Training document for the company-wide automation solution Totally Integrated Automation (T I A) MODULE C1 T I A Training document Page 1 of 66 Module C1 This document was provided by Siemens A&D SCE (automation