B-5
ET 200U Distributed I/O Station
EWA 4NEB 812 6087–02b
Object list Data communications on the bus cannot commence unless the FMS
master is informed of the stations involved and their significance and
structure. This information is contained in the object list (OV).
The object list of the ET 200U(DP Standard/FMS) contains the follo-
wing:
Input and output values of the ET 200U(DP Standard/FMS)
Diagnostics data
Parameter data.
Octet Octet is a general expression for one byte.
OV ³ Object list
P
Page addressing Multiplying of address range
Passive nodes They may exchange data with an active node only after being reque-
sted to do so by the active node (= slave station).
PDU ³ Protocol Data Unit
PII ³ Process image
PIQ ³ Process image
Process image An “image” of the input states (= PII) or output states (= PIQ) at a spe-
cified point of time. The process image can be accessed by the PLC
program.
PROFIBUS PROcess FIeld BUS, German process and field bus standard defined in
the PROFIBUS standard (DIN 19245).
It specifies functional, electrical and mechanical characteristics for a
bit–serial field bus system.
PROFIBUS–DP PROFIBUS–DP draft standard (DIN 19245, Part 3) on which the
ET 200 distributed I/O system is based.
The major task of PROFIBUS–DP is the fast cyclic data exchange
between the central master stations and the I/O devices.
Protective conductor A conductor required for protective measures against shock currents. It
is symbolized by PE.
Protocol Data Unit A protocol data unit (PDU) contains the information to be exchanged
between two bus nodes.
In the PROFIBUS specification, this means a message exchanged, for
example, between the ET 200U(DP Standard/FMS) and the FMS ma-
ster.
The maximum length of a protocol data unit is specified in the ³ list
of communications links.
R
Reference earth ³ Earth
Reference potential Potential to which the voltages of the circuits involved are referred, or
with reference to which they are measured.
Repeater Device for amplifying bus signals and interfacing ³ segments for cov-
ering long distances.
Glossary
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