Siemens S7-1200 System Manual page 8

Table of contents
3.4 Wiring guidelines ......................................................................................................................... 70
4 PLC concepts ....................................................................................................................................... 77
4.1 Execution of the user program .................................................................................................... 77
4.1.1 Operating modes of the CPU ...................................................................................................... 81
4.1.2 Processing the scan cycle in RUN mode .................................................................................... 85
4.1.3 Organization blocks (OBs) .......................................................................................................... 85
4.1.3.1 Program cycle OB ....................................................................................................................... 86
4.1.3.2 Startup OB................................................................................................................................... 86
4.1.3.3 Time delay interrupt OB .............................................................................................................. 87
4.1.3.4 Cyclic interrupt OB ...................................................................................................................... 87
4.1.3.5 Hardware interrupt OB ................................................................................................................ 87
4.1.3.6 Time error interrupt OB ............................................................................................................... 88
4.1.3.7 Diagnostic error interrupt OB ...................................................................................................... 89
4.1.3.8 Pull or plug of modules OB ......................................................................................................... 91
4.1.3.9 Rack or station failure OB ........................................................................................................... 92
4.1.3.10 Time of day OB ........................................................................................................................... 92
4.1.3.11 Status OB .................................................................................................................................... 93
4.1.3.12 Update OB................................................................................................................................... 93
4.1.3.13 Profile OB .................................................................................................................................... 94
4.1.3.14 Event execution priorities and queuing ....................................................................................... 94
4.1.4 Monitoring and configuring the cycle time ................................................................................... 97
4.1.5 CPU memory ............................................................................................................................... 99
4.1.5.1 System and clock memory ........................................................................................................ 101
4.1.6 Diagnostics buffer ..................................................................................................................... 103
4.1.7 Time of day clock ...................................................................................................................... 104
4.1.8 Configuring the outputs on a RUN-to-STOP transition ............................................................. 104
4.2 Data storage, memory areas, I/O and addressing .................................................................... 105
4.2.1 Accessing the data of the S7-1200 ........................................................................................... 105
4.3 Processing of analog values ..................................................................................................... 110
4.4 Data types ................................................................................................................................. 110
4.4.1 Bool, Byte, Word, and DWord data types ................................................................................. 111
4.4.2 Integer data types ..................................................................................................................... 112
4.4.3 Floating-point real data types .................................................................................................... 112
4.4.4 Time and Date data types ......................................................................................................... 113
4.4.5 Character and String data types ............................................................................................... 114
4.4.6 Array data type .......................................................................................................................... 116
4.4.7 Data structure data type ............................................................................................................ 117
4.4.8 PLC data type ........................................................................................................................... 117
4.4.9 Pointer data types ..................................................................................................................... 118
4.4.9.1 "Pointer" pointer data type ........................................................................................................ 118
4.4.9.2 "Any" pointer data type .............................................................................................................. 119
4.4.9.3 "Variant" pointer data type ........................................................................................................ 120
4.4.10 Accessing a "slice" of a tagged data type ................................................................................. 121
4.4.11 Accessing a tag with an AT overlay .......................................................................................... 122
4.5 Using a memory card ................................................................................................................ 124
4.5.1 Inserting a memory card in the CPU ......................................................................................... 125
4.5.2 Configuring the startup parameter of the CPU before copying the project to the memory
card ........................................................................................................................................... 127
4.5.3 Transfer card ............................................................................................................................. 127
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S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG