Siemens SIMATIC S7-300 Manual page 114

Glossary
Execution level
Execution levels form the interface between the operating system of the CPU and the user
program. The sequence for executing the blocks of the user program is specified in the
execution levels.
Flag
Flags are part of the CPU's system memory. They store intermediate results of calculations.
They can be accessed in bit, byte, word or double word operations.
Force
The force function can be used to assign fixed values to specific variables of a user program
or CPU (also: inputs and outputs).
In this context, please note the limitations listed in the
in the Test Functions, Diagnostics and T oubleshooting chapter in the S7-300 Installation
manual
Function
According to IEC 1131-3, a function (FC) is a code block without static data. A function
allows transfer of parameters in a user program. Functions are therefore suitable for
programming frequently occurring complex functions, e.g. calculations.
Function block
According to IEC 1131-3, a function block (FB) is a code block with static data. An FB
enables the transfer of parameters in the user program. Function blocks are therefore
suitable for programming frequently occurring complex functions, e.g. controls, mode
selections.
GD circuit
A GD circuit comprises a number of CPUs sharing data by means of global data
communication, and is used as follows:
• A CPU sends a GD packet to the other CPUs.
• A CPU sends and receives a GD packet from another CPU.
A GD circuit is identified by a GD circuit number.
GD element
A GD element is generated by assigning shared global data. It is identified by a unique
global data ID in the global data table.
GD packet
A GD packet can consist of one or more GD elements transmitted in a single message
frame.
Glossary-4
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Overview of the test functions section
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S7-300 CPU Data: CPU 315T-2 DP
Manual, 12/2005, A5E00427933-02