Siemens Simatic S7-300 Technical Data Manual page 223

Function block
According to IEC 1131-3, a function block (FB) is a --> code block with --> static data. An FB
allows the user program to pass parameters. Function blocks are therefore suitable for
programming frequently occurring complex functions, e.g. controls, mode selections.
Functional ground
Grounding which has the sole purpose of safeguarding the intended function of electrical
equipment. With functional grounding you short-circuit interference voltage which would
otherwise have an unacceptable impact on equipment.
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 broadcasts 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 several GD elements transmitted in a single message
frame.
Global data
Global data can be addressed from any code block (FC, FB, OB). In particular, this refers to
flag bits M, inputs I, outputs Q, timers, counters and data blocks DB. Global data can be
accessed via absolute or symbolic addressing.
Global data communication
Global data communication is a method of transferring global data between CPUs (without
CFBs).
Ground
The conductive earth whose electrical potential can be set equal to zero at any point.
Ground potential can be different from zero in the area of grounding electrodes. The term
reference ground is frequently used to describe this situation.
Grounding means, to connect an electrically conductive component via an equipotential
grounding system to a grounding electrode (one or more conductive components with highly
conductive contact to earth).
CPU 31xC and CPU 31x, Technical data
Manual, Edition 08/2004, A5E00105475-05
Glossary
Glossary-7