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S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
13-6 A5E00105492-03
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According to IEC 1131-3, a function block is a Æ code block that contains Æ static
data. An FB allows parameters to be passed in the user program. Function blocks
are therefore suitable for programming complex functions, e.g. closed-loop
controls, mode selections, which are repeated frequently.
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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.
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A GD circle encompasses a number of CPUs which exchange 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.
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A GD element is generated by assigning shared Æ global data. It is identified by a
unique global data ID in the global data table.
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A GD packet can consist of one or more GD objects which are transmitted together
in a frame.
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Global data can be addressed by any Æ code block (FC, FB, OB). Individually,
these are markers M, inputs I, outputs Q, timers, counters, and data blocks DB.
Global data can be accessed with either absolute or symbolic access.
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Global data communication is a procedure used to transfer Æ global data between
CPUs (without CFBs).
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The conductive earth whose electrical potential can be set equal to zero at any
point.
Ground potential can be different to zero in the area of grounding electrodes. The
term “reference ground” is frequently used to describe this situation.
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