Siemens SINUMERIK 828D Function Manual page 1094

P4: PLC for SINUMERIK 828D
14.3 Programming
Program
A program (also a program organization unit "POU") is a block for a sequence of commands (including
comments), that the user assembles one after the other using the LAD Editor to solve his particular task. The
user has three types of these POUs at his disposal:
• The main program (MAIN)
There is only one of these. The system calls this in the PLC cycle.
• 256 optional subprograms (SBR_xyz)
Subprograms are used to structure and encapsulate functions.
Once coded, they can be called a multiple number of times.
• Three optional interrupt programs
These are executed with a higher priority at a different location in the PLC cycle and are reserved for special
tasks.
Data block
A data block is a block for data (initial values, actual values) and comments with the following properties:
• The data are saved in precisely the same sequence as specified by the user. This means that the inner
structure of the data block is defined and if several data blocks are created with the same inner structure (i.e.
the same type), then a certain data is always located at a specific location. This location is called offset and is
the relative length in bytes from the beginning of the data block (DB) up to the actual piece of data.
• Initial values can be assigned to the data that they assume after being loaded into the PLC for the first time.
• The actual values of the data can also be read online from the control, changed and also saved with the
project.
1094
Function Manual, 09/2011, 6FC5397-0BP40-2BA0
Basic Functions