Siemens SIMATIC S7 System Manual page 6

Table of contents
4 PLC concepts ....................................................................................................................................... 69
4.1 Execution of the control logic ................................................................................................. 69
4.1.1 Reading the inputs and writing to the outputs ........................................................................ 71
4.1.2 Immediately reading or writing the I/O ................................................................................... 71
4.1.3 Executing the user program ................................................................................................... 72
4.2 Accessing data ....................................................................................................................... 74
4.2.1 Accessing memory areas ....................................................................................................... 75
4.2.2 Format for Real numbers ....................................................................................................... 82
4.2.3 Format for strings ................................................................................................................... 82
4.2.4 Assigning a constant value for instructions ............................................................................ 83
4.2.5 Addressing the local and expansion I/O ................................................................................ 83
4.2.6 Using pointers for indirect addressing.................................................................................... 84
4.2.7 Pointer examples ................................................................................................................... 87
4.3 Saving and restoring data ...................................................................................................... 89
4.3.1 Downloading project components .......................................................................................... 89
4.3.2 Uploading project components .............................................................................................. 92
4.3.3 Types of storage .................................................................................................................... 93
4.3.4 Using a memory card ............................................................................................................. 94
4.3.5 Inserting a memory card in a standard CPU .......................................................................... 96
4.3.6 Transferring your program with a memory card ..................................................................... 97
4.3.7 Restoring data after power on ................................................................................................ 99
4.4 Changing the operating mode of the CPU ........................................................................... 100
4.5 Status LEDs ......................................................................................................................... 101
5 Programming concepts ........................................................................................................................ 103
5.1 Guidelines for designing a PLC system ............................................................................... 103
5.2 Elements of the user program .............................................................................................. 105
5.3 Creating your user program ................................................................................................. 108
5.3.1 Earlier versions of STEP 7-Micro/WIN projects ................................................................... 108
5.3.2 Using STEP 7-Micro/WIN SMART user interface ................................................................ 110
5.3.3 Using STEP 7-Micro/WIN SMART to create your programs ............................................... 111
5.3.4 Using wizards to help you create your control program....................................................... 112
5.3.5 Features of the LAD editor ................................................................................................... 113
5.3.6 Features of the FBD editor ................................................................................................... 114
5.3.7 Features of the STL editor ................................................................................................... 114
5.4 Data block (DB) editor .......................................................................................................... 115
5.5 Symbol table ........................................................................................................................ 118
5.6 Variable table ....................................................................................................................... 121
5.7 PLC error reaction ................................................................................................................ 127
5.7.1 Non-fatal errors and I/O errors ............................................................................................. 128
5.7.2 Fatal errors ........................................................................................................................... 129
5.8 Program edit in RUN mode .................................................................................................. 130
5.9 Features for debugging your program ................................................................................. 132
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System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART