Fbs And Fcs Make Programming The Modular Tasks Easy - Siemens SIMATIC S7-1200 Manual

Programming made easy
6.1 Easy to design your user program
Creating additional OBs
You can create multiple OBs for your user program, even for the program cycle and startup
OB events. Use the "Add new block" dialog to create an OB and enter a name for your OB.
If you create multiple program cycle OBs for your user program, the CPU executes each
program cycle OB in numerical sequence, starting with the program cycle OB with the lowest
number (such as OB 1). For example: after the first program cycle OB (such as OB 1)
finishes, the CPU executes the program cycle OB with the next higher number.
Configuring the properties of an OB
Note
Note that you can assign a process image part number to an OB that corresponds to PIP0,
PIP1, PIP2, PIP3, or PIP4. If you enter a number for the process image part number, the
CPU creates that process image partition. See the topic "Execution of the user program
(Page 53)" for an explanation of the process image partitions.
6.1.2

FBs and FCs make programming the modular tasks easy

A function (FC) is like a subroutine. An FC is a code block that typically performs a specific
operation on a set of input values. The FC stores the results of this operation in memory
locations. Use FCs to perform the following tasks:
● To perform standard and reusable operations, such as for mathematical calculations
● To perform functional tasks, such as for individual controls using bit logic operations
An FC can also be called several times at different points in a program. This reuse simplifies
the programming of frequently recurring tasks.
Unlike an FB, an FC does not have an associated instance DB. The FC uses its temp
memory (L) for the data used to calculate the operation. The temporary data is not saved. To
store data for use after the execution of the FC has finished, assign the output value to a
global memory location, such as M memory or to a global DB.
90
You can modify the properties of an
OB. For example, you can configure the
OB number or programming language.
Manual, 03/2014, A5E02486774-AF
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