profibus-fms

Transcription

profibus-fms

Lecture 4 – Profibus
Urban Bilstrup
Urban.Bilstrup@ide.hh.se
Profibus – Outline
 Introduction
 Profibus-DP
• Physical Layer
• Link Layer
• Application Layer
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Profibus – Introduction
Three different versions of PROFIBUS exist:
 PROFIBUS-FMS (Fieldbus Message Specification) is used
based on the Client-Server model for the communication
between automation devices (control level).
 PROFIBUS-DP (Decentralized Periphery) is used for fast
remote inputs and outputs, to connect sensors and actuators to
a controlling device.
 PROFIBUS-PA (Process Automation) is used for the connection
of field devices and transmitters to a process control device. It
allows intrinsic safe transmission and power on the line.
Parameters and function blocks are defined covering the need
of the process engineering.
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Profibus – Introduction
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PROFIBUS-DP-Introduction
PROFIBUS-DP (Decentralized Periphery)
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PROFIBUS-DP-Introduction
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Profibus-DP – Physical layer
 PROFIBUS networks can be set up as either a line or a
tree topology. Passive branch lines should be avoided.
 A maximum of 32 stations (1 master and 31 slaves) can
be connected in one PROFIBUS network segment.
 If more than 32 stations are required, repeaters must be
used to create appropriate segments. It is recommended
that no more than 4 repeaters are used within a network,
because these cause signal delay, a maximum of 126
stations are allowed in total.
 When used, repeaters count as stations on the bus,
although they do not require an address of their own.
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Three alternative connections are possible for RS485 transmission using degree of protection
IP65/67:
 M12 circular connector according to IEC 947-
5-2
 HAN-BRID connector according to DESINA
recommendations
 Siemens hybrid connector
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 Shielded twisted pair, optic fiber, manchester bus powered (MBP).
 Various transmission rates 9.6 kbit/s up to 12 Mbit/s.
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Transmission rate
Maximum length per segment
9.60 kbit/s
1200 m
19.20 kbit/s
1200 m
45.45 kbit/s
1200 m
93.75 kbit/s
1200 m
187.50 kbit/s
1000 m
500,75 kbit/s
400 m
1500,75 kbit/s
200 m
3000,75 kbit/s
100 m
6000,75 kbit/s
100 m
12000,75 kbit/s
100 m
Profibus-DP – Link layer
 At the link protocol level, ProfiBus and its versions
DP-V0, DP-V1 and DP-V2 offer a broad spectrum of
services, which enables optimum communication for
different applications.
 DP-V0 is the cyclic master-slave polling, which is
time deterministic .
 DP-V1 adds acyclic communication for parameter
assignment, configuration, and alarm handling.
 DP-V2 isochronous slave mode and direct slave-toslave communication.
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 A Profibus-DP system uses a bus master to poll slave devices
distributed in a multi-drop fashion on EIA-485.
 A Profibus-DP slave is any pheripheral device (I/O transducer,
valve, network drive, or other meassuring device) which process
information and sends it to the master.
 Profibus-DP supports monomaster and multimaster systems
 In a multimaster system each master represents an independent
subsystem
 The masters are coordinating themselves by passing a token
from one master to the next master and so forth.
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 DP master Class 1 (DPM1) is a central controller that
cyclically exchange information with the distributed slaves.
• Tyical devices are PLCs or PCs
 DP master Class 2 (DPM2) is a device for configuring,
maintenance and diagnostics.
• Tyical devices are laptops equipped with software for
configuration, maintenance and diagnostics.
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 The acyclic (DP-V1) forms the key parameterization
and calibration of the field devices over the bus
during runtime and the introduction of confirmed
alarm messages.
 Transmission of acyclic data is performed parallel to
cyclic data with lower priority often with a master
class 2 device.
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 Adressing with slot and index is used for both cyclic
and acyclic data.
 When addressing specific data, Profibus assumes
that the hardware is modular or can be structured in
functional units, so called modules.
 The slot number adresses the module and the index
number adresses the specific data structure.
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Profibus-DP – Application layer
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 The Profibus DP communication profile protocol
(application layer) comprises two fundamental
applications, namely the user-interface and the direct
data link mapper.
 The user-interface represents the core of the protocol and
is responsible for the correct execution of all operations
foreseen by the standard.
 The direct data link mapper has the task of mapping the
requests coming from the user-interface onto FDL
services; for this purpose, it uses two different services,
namely the Send and Request Data with reply (SRD)
and the Send Data with No acknowledge (SDN).
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 SRD is a confirmed connectionless service which
allows for the sending of up to 246 octets; the
response frame of such a service can also carry up to
246 octets of data.
 SRD is used for all the Profibus DP functions which
involve data transmission between master and
slaves, such as cyclic data exchange, diagnostic,
parameterisation, acyclic read and write, etc.
 SDN is a non-confirmed connectionless service
which is used by the Profibus DP protocol in order to
issue global control commands from master to slave.
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 The FDL services used by the user interface can either be of high or
low priority depending on the Profibus DP functions they implement.
For example, a master implementing the cyclic data exchange function
uses a high-priority SRD frame to send the output values to a slave.
 The latter responds with a low priority SRD frame carrying the input
data. The only exception to such a rule is when the slave has to signal
the presence of a diagnostic message: in this case, it responds with a
high-priority SRD frame.
 FDL users different from the DP protocol could either be the FMS
protocol or, more generally, applications using the FDL services.
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Profibus-FMS – Application layer
PROFIBUS-FMS (Fieldbus Message Specification)
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 The FMS Communication Profile is designed for
communication at cell level. At this level, programmable
controllers (PLCs and PCs) communicate primarily with
each other.
 In this application area a high degree of functionality is
more important than fast system reaction times.
 The communication model of Profibus-FMS is based on
the definition of a Virtual Field Device. This is the part of
a device that is reachable by the communication system.
 The PROFIBUS-FMS communication model permits
distributed application processes to be unified into a
common process by using communication relationships.
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 All accessible values, variables are listed in a so called object
dictionary, which itself can be read out over the bus.
 The object dictionary holds index, name, type of each variable.
 That portion of an application process in a field device which can be
reached via communication is called a virtual field device (VFD).
 All communication objects of an FMS device are entered in the
object dictionary (OD).
 The object dictionary contains description, structure and data type, as
well as the relationship between the internal device addresses of the
communication objects and their designation on the bus (index/name).
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The FMS application layer consists of the following´parts:
 The Fieldbus Message Specification (FMS)
 The Lower Layer Interface (LLI)
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 Static communication objects are entered in the
static object dictionary.
 They are configured once and cannot be modified
during operation.
 FMS recognizes five types of communication objects:
•
•
•
•
•
Simple Variable
Array (series of simple variables of the same type)
Record (series of simple variables of different types)
Domain
Event (event message)
 Dynamic communication objects are entered in the
dynamic section of the object dictionary. These can
be modified during operation.
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 Logical addressing is the preferred method of addressing
for the objects. Accessing is performed with a short
address (the index).
 Confirmed services can only be used for connection-
oriented communication relationships.
 Unconfirmed services can also be used on
connectionless communication relationships (broadcast
and multicast).
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 Context Management services are for establishing
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and terminating logical connections.
Variable Access services are used to access
variables, records, arrays or variable lists.
Domain Management services are used to transmit
large memory areas. The data must be divided into
segments by the user.
Program Invocation Management services are
used for program control.
Event Management services are used to transmit
alarm messages. These messages can also be sent
as broadcast or multicast transmissions.
 VFD Support services are used for identification and
status polling. They can also be sent spontaneously at the
request of a device as multicast or broadcast
transmissions.
 OD Management services are used for read and write
access to the object dictionary.
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profibus-fms

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