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5 PROFIBUS
5.1 Overview PROFIBUS
PROFIBUS was developed as an open fieldbus. It was standardized in the German standard DIN 19
245 and was later standardized in IEC 61158. PROFIBUS is a medium for pure data transfer, like the
RS232 standard for instance.
There are two different types of communication
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Cyclical services PROFIBUS DP (Distributed Peripheral)
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Acyclical services PROFIBUS DPV1 (optional services)
PROFIBUS DP (Distributed Peripheral) is a PROFIBUS version designed to satisfy the requirements
of high-speed, efficient data transfer between a controller (PLC / PC) and remote peripheral devices.
Physical design: Similar to RS 485
A DP system normally consists of one master and up to 126 slaves with the use of repeaters. In
systems employing multiple masters, each master has its own permanently assigned slaves.
Master:
A DP master exchanges data with the slaves via PROFIBUS DP and monitors the bus. It
transfers the data between the higher-level controller and the remote peripheral devices.
Slave:
The DP slaves form the link to the measurement equipment. They condition the input data from
the measurement application for communication with the master, and condition the output data
(control signals) from the master for forwarding to the measurement electronics
The PROFIBUS uses the master-slave technique for data transfer. The master reads the input data
cyclically from the slaves and writes the output data to the slaves.
PROFIBUS DP features
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Transfer rate of 9.6 kBaud to 12 MBaud
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Fast response times and high interference immunity
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Master and slave diagnostics
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Individual slaves can fail or be switched off without interfering with bus operation.
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The whole bus configuration is saved in the master.
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Each slave has a manufacturer-specific ID assigned by the
PI
.
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The slaves are specified by the device description data (GSD file). This file is
imported into the configuration software, simplifying slave configuration.
PROFIBUS DP data transfer
The master always transfers the same number of data bytes with each of its slaves in turn (always
around a loop), thereby always keeping the total transfer time constant.
Each slave must respond within a fixed time slot.
Theoretically, 240 bytes are possible in each response.
The slave must always reply with the same data length.
