Siemens Simatic S7-300, Hardware And Installation Manual, Page: 226 / 242

Glossary
S7-300 Programmable Controller Hardware and Installation
12-6
A5E00105492-01
Galvanically isolated
The reference potential of the control and on-load power circuits for isolated I/Os is
galvanically isolated; e.g. by optocouplers, relay contact or transformer. I/O circuits
can be connected to a common potential.
GD circuit
A GD circuit consists of a number of CPUs exchanging data by means of global
data communication and which are used as follows:
•
One CPU broadcasts a GD packet to the other CPUs.
•
One 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 multiple --> GD elements transferred in a single
message frame.
Global data communication
Global data communication is a procedure used for --> global data exchange
between CPUs (no CFBs).
Ground (to)
To ground means to connect an electrically conducting component to the
grounding electrode (one or more conducting components which have a very good
contact with the earth) across a grounding system.
Ground
The conducting earth whose electrical potential can be set equal to zero at any
point.
In the vicinity of grounding electrodes, the earth can have a potential different to
zero. The term "reference ground" is frequently used to describe these
circumstances.
GSD file (device master file)
The device master file (GSD file) stores all slave specific properties. The GSD file
format is specified in EN 50170,Volume 2, PROFIBUS.