Siemens SIMATIC S7-300 Series Reference Manual page 177
Cpu specifications
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Functional grounding
Grounding which has the sole purpose of safeguarding the intended function of
the electrical equipment. Functional grounding short-circuits interference voltage
which would otherwise have an impermissible impact on the equipment.
GD circuit
A GD circuit encompasses a number of CPUs which exchange data by means of
global data communication. They are used as follows:
S A CPU broadcasts a GD packet to the other CPUs.
S 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 ³ global data. It is uniquely
identified in the global data table by its GD ID.
GD Packet
A GD packet can consist of one or multiple ³ GD elements transmitted in a
single message frame.
Global data
Global data can be addressed from any ³ code block (FC, FB, OB). In detail,
this refers to memory bits M, inputs I, outputs Q, timers, counters and data
blocks (DBs). Absolute or symbolic access can be made to global data.
Global data communication
Global data communication represents a method ³ for exchanging global data
between CPUs (without CFBs).
Ground
The conductive 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.
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01
Glossary
Glossary-7
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