Спецификация протокола Profibus

Page 21

PROFIBUS-Specification-Normative-Parts-2:1997

MC Message Cycle

mp Number of Retries per Poll List

MSAP Management Service Access Point the MSAP used by this station's

FMA1/2 entity for communication with other FMA1/2 entities

MSB Most Significant Bit of a field or octet

mt Number of Retries per token rotation

n Number of Stations

na Number of Active (Master) Stations

NA No Acknowledgement/response

NIL locally existing value, but not fixed in this standard

NO Not OK (L/M_status of the service primitive)

np Number of Slave (passive) Stations

NR No Response FDL/FMA Data acknowledgement negative & send data ok

(L/M_status of the service primitive)

NRZ Non-Return-to-Zero (PHY), an encoding technique where transitions

occur only when successive data bits have different values

NS Next Station (FDL), the station to which this Master will pass the

token

OK Service finished according to the rules (L/M_status of the service

primitive)

OSI Open Systems Interconnection

PBC PROFIBUS Controller

PC Programmable Controller

PHY PHYsical layer, OSI layer 1

PI Parallel Interface

PON Power ON transition occurs at a station

PS Previous Station (FDL), the station which passes the token to this

Master station

R Receiver (PHY)

R

d

pulldown Resistance to DGND of bus terminator

RAM Random Access Memory

RDH Response FDL Data High and no resource for send data (L/M_status

of the service primitive)

RDL Response FDL/FMA1/2 Data Low and no resource for send data

(L/M_status of the service primitive)

RET RETry

REP REPeater, a device that extends the distance and number of

stations supported by a PROFIBUS System

req request primitive

Res Reserved

Page 22

PROFIBUS-Specification-Normative-Parts-2:1997

R

u

pullup Resistance to VP of bus terminator

RP Reserved Power

RR no Resource for send data and no Response FDL data (acknowledge-

ment negative), (L/M_status of the service primitive)

RS no Service or no Rem_add activated at Remote service access

point(acknowledgement negative), (L/M_status of the service primi-

tive)

RSAP Reply Service Access Point an LSAP at which Request Data may be

obtained

R

SYS

Rate SYStem total message cycles rate at which confirmed FDL

Transactions are performed

R

t

line termination Resistance of bus terminator

RxD Received Data signal (PHY, RS-485)

S Slave station, this station can never hold the token, a reduced

function station, its FDL User may only respond to requests from

initiating FDL Users in Master stations

SA Source Address of a frame

SAE Source Address Extension(s) of a frame conveys SSAP and/or source

Bus ID

SAP Service Access Point, the point of interaction between entities in

different protocol layers

SC Single Character acknowledge frame

SD Start Delimiter of a frame

SDA Send Data with Acknowledge (FDL Service)

SDN Send Data with No acknowledge (FDL Service)

SI Serial Interface

SRD Send and Request Data with reply (FDL Service)

SSAP Source Service Access Point, an LSAP which identifies the local

FDL User which initiates a transaction

Stn Station, a device with an FDL Address on this PROFIBUS System

SYN SYchroNizing bits of a frame (period of IDLE) it guarantees the

specified frame integrity and allows for receiver synchronization

t

BIT

BIT Time, FDL symbol period the time to transmit one bit on this

PROFIBUS System; 1/Data Signalling Rate in bit/s

T Transmitter

T

A/R

Time to transmit an Acknowledgement/Response frame

TC Token Cycle, cycle to transmit a token frame

T

GUD

GAP UpDate Time, the time this Master station waits between suc-

cessive GAP maintenance cycles

Page 23

PROFIBUS-Specification-Normative-Parts-2:1997

T

ID

IDle Time, the time a Master station must wait between the last

bit of a transmitted or received frame and the first bit of the

next frame it transmits; this creates the interframe SYNchronizing

period of IDLE

T

MC

Message Cycle Time, the time between transmission of the first bit

of an action frame and receipt of the last bit of the correspond-

ing reply frame

T

QUI

QUIet Time, Transmitter fall Time (Line State Uncertain Time)

and/or Repeater switch Time; the time a transmitting station must

wait after the end of a frame before enabling its receiver

T

RDY

ReaDY Time, the time after which the transmitting Master will

reply frame

T

RR

Real Rotation Time, the time between the last successive recep-

tions of the token by this Master station

TS This Station

T

SDI

Station Delay of Initiator, the time this Master station will wait

before sending successive frames

T

SDR

Station Delay of Responder, the actual time this responder waits

before generating a reply frame

T

SET

SETup Time, the time between an event (e.g. interrupt SYN timer

expired) and the necessary reaction (e.g. enabling receiver)

T

SL

SLot Time, the maximum time a Master station must wait for a

transaction response

T

SM

Safety Margin Time

T

SR

System Reaction Time, the target maximum time to complete all

transactions (including retries) in one poll cycle in single

Master PROFIBUS Systems

T

S/R

Send/Request frame Time, the time to transmit a send/request frame

T

SYN

SYNchronization Time,the period of IDLE in front of frames after

which this station enables its receiver; the required minimum

inter-frame IDLE period to guarantee frame integrity and a valid

frame

T

SYNI

SYNchronization Interval Time, the maximum time that a receiving

station waits for the required inter-frame IDLE period, of dura-

tion T

SYN

, to occur before it detects a bus fault

T

TC

Token Cycle Time, the time to pass the token to the next Master

station in the absence of errors

T

TD

Transmission Delay Time, the maximum delay experienced between one

station's transmitter and any other station's receiver

T

TF

Token Frame Time, the time to transmit the token frame

T

TH

Token Holding Time, the remaining period which this current Master

station is allowed to initiate transactions during this token

round

TTL Transistor Transistor Logic

Page 24

PROFIBUS-Specification-Normative-Parts-2:1997

T

TO

Time-Out Time, the period of IDLE after which this Master station

will claim the (lost) token, or any station will report a time-out

fault to its FMA User, depends on this station's FDL Address

T

TR

Target Rotation Time, the anticipated time for one token round,

including allowances for high and low priority transactions,

errors and GAP maintenance

TTY Tele-TYpe

TxD Transmit Data signal (PHY, RS-485)

UART Universal Asynchronous Receiver/Transmitter

UC UART Character

UE negative acknowledgement, remote User interface Error (L/M_status

of the service primitive)

µP Microprocessor

VDE Verband Deutscher Elektrotechniker (Society of German Electronics

Engineers)

VP Voltage Plus

1 Chip MC Single Chip MicroComputer

3.2 Basic Properties

The PROFIBUS Specification defines the technical and functional characteristics

of a serial fieldbus which is aimed at the inter-connection of digital field

devices or systems with low or medium performance, e.g. sensors, actuators,

transmitters, programmable logical controllers (PLC), numerical controllers

(NC), programming devices, local man machine interfaces etc.

Often a field control system is based on a central control and supervision unit,

which is connected to a number of devices and small systems distributed in the

field. In such cases the dominant data transfer is centrally oriented and cyclic

from the field devices to the central data processing unit or to a superior

control system.

The system contains master stations and slave stations. A master is able to con-

trol the bus, i.e. it may transfer messages without remote request when it has

the right of access (called token). In contrast to this a slave is only able to

acknowledge a received message or to transfer data after a remote request.

The token circulates in a logical ring formed by the masters. If the system con-

tains only one master, e.g. a central control and supervision station, no token

passing is necessary. This is a pure single-master/n-slave system. The minimum

configuration comprises one master and one slave, or two masters.

The Physical Layer (this is the medium, including lengths and topology, the line

interface, the number of stations and the transmission speed, variable in the

range from 9,6 to 1500 kbit/s) can be adapted to different applications. However

there is a common access method and transmission protocol and there are common

services at the user interface.

Page 25

PROFIBUS-Specification-Normative-Parts-2:1997

3.3 Characteristic Features

The various application fields, e.g. process control, factory automation, power

distribution, building automation, primary process industry etc., have the fol-

lowing characteristic bus requirements:

Network topology Linear bus with or without terminator, including drop

cables and branches (tree)

Medium, distances,

number of stations

Depending on the signal characteristics, e.g. for

shielded twisted pair,

≤ 1,2 km without repeaters, 32 stations

Transmission speed Depending on network topology and line lengths, e.g.

step-wise from 9,6 to 1500 kbit/s

Redundancy Second medium is optional

Transmission charac-

teristics

Halfduplex, asynchronous, slip protected synchroniza-

tion (no bit stuffing)

Addressing 0 to 127 (127 = global addresses for broad-cast and

multicast messages), address extension for regional ad-

dress, segment address and Service Access address

(Service Access Point, LSAP), 6 bit each

Station types Masters (active stations, with bus access control);

Slaves (passive stations, without bus access control);

preferably at most 32 masters, optionally up to 127, if

the applications are not time critical

Bus access Hybrid, decentral/central; token passing between master

stations and master-slave between master and slave sta-

tions

Data transfer services Acyclic:

Send Data with/without Acknowledge

Send and Request Data with Reply

Cyclic (Polling):

Send and Request Data with Reply

Frame length 1 or 3 to 255 byte per frame, 0 to 246 layer 2 data oc-

tets for each Data Unit without address extension

Data integrity Messages with Hamming distance (HD)=4, sync slip detec-

tion, special sequence to avoid loss and multiplication

of data

Page 26

PROFIBUS-Specification-Normative-Parts-2:1997

3.4 Scope

This part of the specification deals with "Layer 0" and Layer 1 (Physical Media

and Physical Layer PHY, according to the ISO-OSI Layer Model) which describe the

medium and signal characteristics; furthermore Part 3 and 4 defines the Layer 2

(Fieldbus Data Link Layer, FDL), containing the transmission protocol and Medium

Access Control, as well as the Interface Services (FDL/User Interface Services)

used by the Layer 7 (Application Layer APP) immediately above. Finally the man-

agement of the Layers 1 and 2 (FMA1/2), including the user services, is covered

(cf. Fig. 1).

In order to achieve high efficiency and throughput as well as low hardware and

software costs the Layers 3 to 6 (Network, Transport, Session, Presentation) are

left empty. A few relevant functionalities of these layers are realised in

Layer 2 or in Layer 7.

The Application Layer functionalities (APP) and the related management (FMA7)

are specified in Part 5, 6 and 7 of this specification.

It is intended to specify different Physical Layers to meet the requirements of

various applications. All present and future variants use the same common Medium

Access Control protocol and transmission protocol (formats, procedures), and

they have a common interface to the Application Layer, including the related

services.

The version 1 Physical Layer uses the US standard EIA RS-485. Further versions

are to be specified in the future.

The octet (character) format is the UART format FT 1.2 (asynchronous transmis-

sion with start-stop synchronization) for Telecontrol Equipment and Systems,

which is specified in IEC 870-5-1.

The transmission protocol definitions are close to the standard IEC 870-5-2,

specified by IEC TC 57.

The Medium Access Control protocol, the data transfer services and the manage-

ment services are guided by the standards DIN 19 241-2, IEC 955(PROWAY C), ISO

8802-2 and ISO/IEC JTC 1/SC 6N 4960 (LLC type 1 and LLC type 3). The complete

protocol takes into consideration the high data integrity requirements of

process data transmission.

Appendix A explains possible structures of repeaters and fieldbus devices as

well as a topology with a single master station serving several fieldbus lines.

Some guidelines on a redundant central control unit and a bus analyser/

diagnostic unit are added. Finally the data transfer rate and the system

reaction time is calculated for an example.

Page 27

PROFIBUS-Specification-Normative-Parts-2:1997

PROFIBUS User

+-----------------------+--------+

Layer ! Application, App ! FMA7 ! Part 6 and 7

7 ! ! !

----------- +-----------------------+--------+

Layer ! Presentation "Null" ! !

6 ! ! !

+-----------------------+ !

Layer ! Session "Null" ! !

5 ! ! !

+-----------------------+ "Null" !

Layer ! Transport "Null" ! !

4 ! ! !

+-----------------------+ !

Layer ! Network "Null" ! !

3 ! ! !

+-----------------------+--------+

FDL-User FMA1/2 User

----------- +-----------------------+--------+ <-- clause 4

\

! Interface Services ! M <-!---- clause 5 +---- Part 3

Layer ! ! A !

2 ! Medium Access Control ! N ! <--+-------------- Part 4

! Transmission Protocol ! A M ! <--

/

! (FDL) ! G E !

----------- +-----------------------+ E N ! <-- clause 4.2 \

Layer ! ! T ! !

1 ! Physical Layer (PHY) ! ! <-- clause 4.1 !

! !(FMA1/2)! >- Part 2

----------- +----------+---+--------+--------+ !

-----------+ +------------------ !

"Layer 0" Transmission Medium <-- clause 4.1 /

----------------------------------

FMA7 : Fieldbus Management Layer 7

FMA1/2: Fieldbus Management Layers 1 and 2

FDL : Fieldbus Data Link

PHY : Physical

Figure 1. ISO Layer Model

4 Data Transmission (Physical Media, Physical Layer)

In order to cover a variety of requirements regarding topology, line length,

number of stations, data transfer rate and protection against environmental

influences, several Physical Layer versions are supported:

Version 1:

NRZ bit encoding is combined with EIA RS-485 signalling, targeted to low cost

line couplers, which may or may not isolate the station from the line (galvanic

isolation); line terminators are required, especially for higher date rates (up

to 1500 kbit/s).

Version 2:

Flexible topology, covering a large area (tree topology), line couplers which

consume less power and which reduce the influence of defective stations on bus

operation, power transmission via the signal conductors, explosive atmosphere

protection (Intrinsic Safety) and improved electromagnetic compatibility, a

Physical Layer conform to IEC 1158-2.

Page 28

PROFIBUS-Specification-Normative-Parts-2:1997

The future versions shall be based on the Layer 1/Layer 2 interface described in

clause 4.2, which includes definitions of the service primitives and the related

parameters as well as the recommendations concerning encoding and signalling.

4.1 Version 1

The version 1 specifications describe a balanced line transmission corresponding

to the US standard EIA RS-485 (EIA: Electronic Industries Association; RS-485:

Standard for electrical characteristics of generators and receivers for use in

balanced digital multipoint systems). Terminators, located at both ends of the

twisted pair cable, enable the version 1 Physical Layer to support in particular

higher speed transmission. The maximum cable length is 1,2 km for data rates ≤

93,75 kbit/s. For 1500 kbit/s the maximum length is reduced to 70/200 m for

Type B/A cable (see subclause "Bus Cable").

4.1.1 Electrical Characteristics

- Topology : Linear bus, terminated at both ends, stubs ≤ 0,3 m, no

branches;

In contrast to the EIA RS-485 recommendations it is

good practice to allow longer stubs, if the total of

the capacities of all stubs (Cstges) does not exceed

the following values:

Cstges ≤ 0,2 nF @ 1500 kbit/s

Cstges ≤ 0,6 nF @ 500 kbit/s

Cstges ≤ 1,5 nF @ 187,5 kbit/s

Cstges ≤ 3,0 nF @ 93,75 kbit/s

Cstges ≤ 15 nF @ 9,6 and 19,2 kbit/s

It shall be taken into consideration that the total

line length includes the sum of the stub lengths.

- Medium : Shielded Twisted Pair, see subclause "Bus Cable"

- Line Length : ≤ 1200 m, depending on the data rate and cable type

- Number of stations : 32 (master stations, slave stations or repeaters)

- Data rates : 9,6 / 19,2 / 93,75 / 187,5 / 500 / 1500 kbit/s,

additionally higher data rates can be supported.

- Transceiver chip : e.g. SN 75176A, DS3695 or others

The line length and number of connected stations may be increased by using

repeaters (bidirectional amplifiers, cf. annex 2-A.1). A maximum of 3 repeaters

between two stations is permissible. If the data rate is ≤ 93,75 kbit/s and if

the linked sections form a chain (linear bus topology, no active star) the maxi-

mum permissible topology assuming wire size 0,22 mm

2

(24 AWG, American Wire

Gauge) is as follows:

Page 29

PROFIBUS-Specification-Normative-Parts-2:1997

1 repeater : 2,4 km and 62 stations

2 repeaters: 3,6 km and 92 stations (cf. Fig. below)

3 repeaters: 4,8 km and 122 stations

Section 1 maximum 31 Stations + 1 Repeater

R

t

-------+----------+----------------------+----------+---R

t

! ! ! !

+-+-+ +-+-+ +-+-+ !

!M/S! !M/S! - - - - - !M/S! ==+==

+---+ +---+ +---+ !REP!

==+==

!

Section 2 maximum 30 Stations + 2 Repeaters !

R

t

--+--------------+-----------------------+----------++--R

t

! ! ! !

! +-+-+ +-+-+ +-+-+

==+== !M/S! - - - - - !M/S! !M/S!

!REP! +---+ +---+ +---+

==+==

!

! Section 3 maximum 31 Stations + 1 Repeater

R

t

--+--------------+-----------------------+-----------+--R

t

! ! !

+-+-+ +-+-+ +-+-+

!M/S! - - - - - !M/S! !M/S!

+---+ +---+ +---+

M/S Master/Slave Station

REP Repeater

R

t

Bus Terminator

Figure 2. Repeater in Linear Bus Topology

In a tree topology more than 3 repeaters may be used and more than 122 stations

may be connected, e.g. 5 repeaters and 127 stations. A large area may be covered

by this topology, e.g. 4,8 km length and data rate ≤ 93,75 kbit/s with wire size

0,22 mm

2

.

Page 30

PROFIBUS-Specification-Normative-Parts-2:1997

+---+ +---+

!M/S! !M/S!

+-+-+ +-+-+

! Section 1 Section 2 !

R

t

--+------------------+--R

t

R

t

--+--------------+--R

t

max. 31 Stn ! ! max. 31 Stn

==+== ==+==

!REP! !REP!

==+== ==+==

! Section 3 !

R

t

--+-+---------+---------+---------+--R

t

! ! max. 28 Stn !

==+== ==+== +-+-+

!REP! !REP! !M/S!

==+== ==+== +---+

Section 4 ! !

R

t

--+-----------------+ R

t

--+

! max. 31 Stn ! ! +---+

+-+-+ R

t

+----!M/S!

!M/S! ! +---+

+---+ !

Section 5 !

max. 30 Stn !

!

R

t

--+

!

Total number of ==+==

Stations on all !REP!

Sections:

127

==+==

! Section 6

+------------------+--R

t

! max. 31 Stn !

R

t

+-+-+

!M/S!

+---+

M/S Master/Slave Station

REP Repeater

R

t

Bus Terminator

Stn Stations

Figure 3. Repeater in Tree Topology

4.1.2 Connector Technique, Mechanical and Electrical Specifications

4.1.2.1 Bus Connector

Each station is connected to the medium via a 9-pin D-sub connector. The female

side of the connector is located in the station, while the male side is mounted

to the bus cable.

The mechanical and electrical characteristics are specified in IEC 807-3.

Preferably a metal connector housing should be used. When put together both

parts of the connector should be fixed by conducting screws.

The connection between the cable sections and the stations should be realised as

T-connectors, containing three 9-pin D-sub connectors (two male connectors and

one female connector). Such T-connectors allow disconnection or replacement of

stations without cutting the cable and without interrupting operation (on line

disconnection).

Спецификация протокола Profibus

Подождите немного. Документ загружается.