Спецификация протокола Profibus

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PROFIBUS-Specification-Normative-Parts-2:1997

4.1.2.2 Contact Designations

The pin assignments for the connectors are shown in Table 1.

Table 1. Contact designations

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

! Pin ! RS-485 ! Signal ! Meaning !

! No ! Ref. ! Name ! !

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

! 1 ! ! SHIELD 2) ! Shield, Protective Ground !

! ! ! ! !

! 2 ! ! M24V 2) ! Minus 24V Output Voltage !

! ! ! ! !

!

3

!

B/B'

!

RxD/TxD-P

!

Receive/Transmit-Data-P

!

! ! ! ! !

! 4 ! ! CNTR-P 2) ! Control-P !

! ! ! ! !

!

5

!

C/C'

!

DGND

!

Data Ground

!

! ! ! ! !

! 6 ! ! VP 1) ! Voltage-Plus !

! ! ! ! !

! 7 ! ! P24V 2) ! Plus 24V Output Voltage !

! ! ! ! !

!

8

!

A/A'

!

RxD/TxD-N

!

Receive/Transmit-Data-N

!

! ! ! ! !

! 9 ! ! CNTR-N 2) ! Control-N !

! ! ! ! !

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

! 1) Signal is only necessary at station at end of the bus cable!

! 2) Signals are optional !

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

RxD/

TxD-P DGND

1 2 3 4 5

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

! o o o o o !

! o o o o !

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

6 7 8 9

RxD/

TxD-N

Figure 4. Connector pinout, front view of male and back view of female

respetively.

The Data Ground, connected to pin 5, and the Voltage Plus, connected to pin 6,

supply the Bus Terminator (cf. subclause 4.1.2.5).

The control signals, connected to pin 4 and pin 9, support direction control

when repeaters without self control capability are used. RS-485 signalling is

recommended. For simple devices the signal CNTR-P may be a TTL signal (1 TTL

load) and the signal CNTR-N may be grounded (DGND). The definition of signalling

is not subject of this specification.

The 24V output voltage, according to IEC 1131-2, allows the connection of

operator panels or service devices without integrated power supply. If a device

offers P24V this P24V shall allow a current load up to 100 mA.

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PROFIBUS-Specification-Normative-Parts-2:1997

4.1.2.3 Bus Cable

The PROFIBUS (version 1) medium is a shielded twisted pair cable. The shield

helps to improve the electromagnetic compatibility (EMC). Unshielded twisted

pair may be used, if there is no severe electromagnetic interference (EMI).

The characteristic impedance of the cable shall be in the range between 100 and

220 Ω, the cable capacity (conductor - conductor) should be < 60 pF/m and the

conductor cross sectional area should be ≥ 0,22 mm

2

(24 AWG). Cable selection

criteria are included in the appendix of the US standard EIA RS-485.

Two types of cables are defined:

Table 2. Cable specifications

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

!Cable Parameter ! Type A ! Type B !

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

!Impedance ! 135 to 165

Ω

! 100 to 130

Ω

!

! ! (f = 3 to 20 MHz) ! (f

>

100kHz) !

!Capacity ! < 30 pF/m ! < 60 pF/m !

!Resistance ! < 110

Ω

/km ! - !

!Conductor area !

≥

0,34 mm

2

(22 AWG) !

≥

0,22 mm

2

(24 AWG) !

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

The following table shows the maximum length of cable Type A and cable Type B

for the different transmission speeds.

Table 1. Cable length for the different transmission speeds

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

! Baud rate ! ! ! ! ! ! !

! [kbit/s] ! 9.6 ! 19.2 ! 93.75 ! 187.5 ! 500 ! 1500 !

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

! Cable Type A ! ! ! ! ! ! !

! Length in m ! 1200 ! 1200 ! 1200 ! 1000 ! 400 ! 200 !

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

! Cable Type B ! ! ! ! ! ! !

! Length in m ! 1200 ! 1200 ! 1200 ! 600 ! 200 ! 70 !

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

The dependency of the permissible data rate upon the network expanse (maximum

distance between two stations) is shown in Fig. 2-A.1 of the US standard EIA RS-

422-A (also included in DIN 66 259 and CCITT V.11).

Note: The recommendations concerning the line length presume a maximum signal

attenuation of 6 dB. Experience shows that the distances may be doubled if

conductors with an area ≥ 0,5 mm

2

(20 AWG) are used.

The minimum wiring between two stations is shown in Fig. 5.

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PROFIBUS-Specification-Normative-Parts-2:1997

Controller 1 Controller 2

RxD/TxD-P 3 o--------------------o 3 RxD/TxD-P

DGND 5 o o 5 DGND

RxD/TxD-N 8 o--------------------o 8 RxD/TxD-N

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

! Shield !

Protective --+-- --+-- Protective

Ground --- --- Ground

- -

NOTE: Inversion of the two wires is not allowed!

Figure 5. Interconnecting Wiring

The wiring shown in Fig. 5 allows a common mode voltage between both stations

(i.e. the voltage difference between the Protective Grounds) of at most ± 7 V.

If a higher common mode voltage is expected, a compensation conductor between

the grounding points shall be installed.

4.1.2.4 Grounding, Shielding

If a shielded twisted pair cable is used it is recommended to connect the shield

to the Protective Ground at both ends of the cable via low impedance (i.e. low

inductance) connections. This is necessary to achieve a reasonable electromag-

netic compatibility.

Preferably the connections between the cable shield and the Protective Ground

(e.g. the metallic station housing) should be made via the metallic housings and

the metallic fixing screws of the sub-D connectors. If this is not possible the

pin 1 of the connectors may be used.

Grounding and shielding shall be according to DIN/VDE 0160 and DIN 57 899/

VDE 0800.

4.1.2.5 Bus Terminator

The bus cable Type "A" and "B" shall be terminated at both ends with R

tA

respectively R

tB

. The termination resistor R

t

specified in EIA-RS-485 shall be

complemented by a pulldown resistor R

d

(connected to Data Ground DGND) and by a

pullup resistor R

u

(connected to Voltage-Plus VP). This supplement forces the

differential mode voltage (i.e. the voltage between the conductors) to a well

defined value when no station is transmitting (during the idle periods).

Each station which is destined to terminate the line (in common with a Bus Ter-

minator) shall make Voltage-Plus (e.g. + 5 V ± 5%) available at pin 6 of the bus

connector.

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PROFIBUS-Specification-Normative-Parts-2:1997

VP (6) o------+

!

+++

! ! R

u

= 390

Ω

+++

!

RxD/TxD-P (3) o------+

!

+++ R

tA

= 220

Ω

! ! resp.

+++ R

tB

= 150

Ω

!

RxD/TxD-N (8) o------+

!

+++

! ! R

d

= 390

Ω

+++

!

DGND (5) o------+

Figure 6. Bus Terminator

Assuming a power supply voltage of + 5 V ± 5% the following resistor values are

recommended:

R

tA

= 220 Ω ± 2%, min. 1/4 W;

R

tB

= 150 Ω ± 2%, min. 1/4 W;

R

u

= R

d

= 390 Ω ± 2%, min. 1/4 W

The power source supplying pin 6 (VP) shall be able to deliver a current of at

least 10 mA within the specified voltage tolerances.

A mixture of both cable types and cable termination resistors as described above

is allowed for a PROFIBUS System. However, the maximum line length has to be

reduced up to the half of the above fixed values if line termination and line

impedance do not match.

4.1.3 Transmission Method

4.1.3.1 Bit Encoding

In the version 1 of the Physical Layer of the PROFIBUS Specification NRZ (Non

Return to Zero) coded data is transmitted via a twisted cable. A binary "1" is

represented by a constant positive differential voltage between pin 3 (RxD/TxD-

P) and pin 8 (RxD/TxD-N) of the bus connector, a binary "0" by a constant

negative differential voltage.

4.1.3.2 Transceiver Control

When a station is not transmitting the transmitter output shall be disabled, it

shall present a high impedance to the line. Preferably this should be controlled

by the "Request to Send" signal (RTS, cf. clause 4.2). During the idle periods,

i.e. when no data is transmitted by any station, the line signal shall represent

a binary "1". Therefore the Bus Terminator shall force the differential voltage

between the connector pins 3 and 8 to be positive when all transmitters are dis-

abled. The line receivers shall always be enabled, therefore during idle the

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PROFIBUS-Specification-Normative-Parts-2:1997

binary signal "1" is received by every station (cf. Part 4, subclause 4.1.7, Syn

time).

4.2 Interface between Physical Layer (PHY) and Medium Access and Transmission

Protocol (FDL)

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

! ! !

Layer 2 !

FDL

! !

! ! !

! ! FMA1/2 !

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

=====================

+ !

! ! !

Layer 1 !

PHY

! !

! ! !

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

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

"Layer 0" Physical Medium

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

Figure 7. Interface between PHY and FDL in Relation to Layer Model

This clause includes an abstract description of the PHY data service. The

service is provided by the PHY Layer to the FDL Layer. It supports reception and

transmission of bits (FDL symbols) which are elements of an UART character (cf.

Part 4, subclause 4.5.1). Each FDL symbol is of duration one bit time t

BIT

(cf.

Part 4, subclause 4.1.7).

The interface description does not specify or constrain the implementation

within a fieldbus entity.

4.2.1 Overview of the Interaction

The PHY data service includes two service primitives. A request primitive is

used to request a service by the FDL controller; an indication primitive is used

to indicate a reception to the FDL controller. The names of the respective

primitives are as follows:

PHY_DATA.request

PHY_DATA.indication

Temporal relationship of the primitives:

station station

1 n

! !

PHY_DATA.req ! !

------------------>! - _ !

! - _ ! PHY_DATA.ind

! - !----------------->

req request ! !

ind indication ! !

Figure 8. PHY Data Service

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PROFIBUS-Specification-Normative-Parts-2:1997

4.2.2 Detailed Specification of the Service and Interaction

This subclause describes in detail the service primitives and the related

parameters in an abstract way. The parameters contain information needed by the

Physical Layer entity.

Parameters of the primitives:

PHY_DATA.request

(FDL_symbol)

- The parameter FDL_symbol shall have one of the following values:

a) ZERO corresponds to a binary "0"

b) ONE corresponds to a binary "1"

c) SILENCE disables the transmitter when no valid FDL symbol is to

be transmitted

The PHY_DATA.request primitive is passed from the FDL Layer to the PHY Layer to

request that the given symbol shall be sent to the fieldbus medium.

The reception of this primitive causes the PHY Layer to attempt encoding and

transmission of the FDL symbol using signalling according to the related PHY

Layer specifications (e.g. according to version 1, clause 4.1).

The PHY_DATA.request is a timed request, which may only be made once per FDL

symbol period (t

BIT

). The PHY Layer may confirm this primitive with a locally

defined confirmation primitive.

PHY_DATA.indication

(FDL_symbol)

- The parameter FDL_symbol shall have one of the following values:

a) ZERO corresponds to a binary "0"

b) ONE corresponds to a binary "1"

The PHY_DATA.indication primitive is passed from the PHY Layer to the FDL Layer

to indicate that a FDL symbol was received from the fieldbus medium. The effect

of receipt of this primitive by the FDL Layer is not specified.

The PHY_DATA.indication is a timed indication, which may be made only once per

received FDL symbol period (t

BIT

).

4.2.3 Electrical Requirements and Encoding

The physical characteristics of the interface between PHY and FDL Layer

(connector type, pin assignment, driver and receiver characteristics etc.) are

not specified. Experience shows that at least the following three signals are

required: Transmitted Data (TxD), Received Data (RxD) and Transmitter Enable

(Request to Send, RTS). An example of signal encoding is as follows:

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PROFIBUS-Specification-Normative-Parts-2:1997

PHY_DATA.request PHY transmit encoding

parameter values TxD RTS

ZERO 0 1

ONE 1 1

SILENCE x 0

x: irrelevant

PHY_DATA.indication PHY receive encoding

parameter values RxD

ZERO 0

ONE 1

The FDL Layer generates its own time frame (FDL symbol period, UART clock). Con-

sequently no time information (transmit/receive clock) is needed from the PHY

Layer.

For certain implementations it may be useful to pass time information from the

PHY Layer to the FDL Layer or vice versa. Furthermore an additional control sig-

nal passed from the FDL Layer to the PHY Layer may be advisable: the Clear to

Send (CTS).

Both functions are not included in the interface specifications. If required

they shall be locally defined.

4.3 Redundancy of Physical Layer and Media (optional)

The use of redundant PHY Layers is supported to improve the reliability of the

fieldbus. When implemented, the redundant PHY Layer contains two separately in-

stalled media (bus a and bus b) and two complete transceivers (transmitter &

receiver) per station. The redundancy architecture is shown in Fig. 9.

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

! Communications !

! Microprocessor !

! !

! LSS ! !

! +-/ -+ UART Controller !

! !

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

RxD-a ^ ^ RxD-b v TxD

! ! !

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

! ! !

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

! ! ! !

+--^-------v--+ +--^-------v--+

! Transceiver ! ! Transceiver !

! a ! ! b !

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

! !

Bus a -----------------+-------------------!------------------

!

Bus b -------------------------------------+------------------

Figure 9. Redundancy of Physical Layer and Media

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PROFIBUS-Specification-Normative-Parts-2:1997

The basic principle, shown in Fig. 9, assumes that data is sent out simultane-

ously by both transceivers onto both media (Bus a and Bus b). In contrast to

this each station receives from only one medium (either Bus a or Bus b). The

receive channel is selected by a Line Selector Switch (LSS), which is located

between both transceivers and the UART controller, or - if two UART controllers

are used - between the UART controllers and the Communications Microprocessor.

The Line Selector Switch is completely controlled by the FDL Layer. For this the

Communications Microprocessor of each station monitors the medium activity, in-

dependently of any other station. The main switching conditions for masters and

slaves are as follows:

- Two or more successive invalid frames are received, i.e. UART characters with

invalid format, invalid parity bit or invalid frame check sequence are

detected.

- Time out timer T

TO

expires, cf. Part 4, subclause 4.1.7.

- No minimum idle period (i.e. line idle for at least T

SYN

) was detected during

one Synchronization Interval Time T

SYNI

, cf. Part 4, subclause 4.1.7.

The selected receive channel a (primary) or b (alternate) is notified to the

Fieldbus Management (FMA1/2, cf. Part 3, clause 4.2). The Fieldbus Management

then provides this information to the local user via the FMA1/2 interface. There

is no preferred receive channel after the system initialization is finished.

Page 39

PROFIBUS-Specification-Normative-Parts-2:1997

Annex 2-A (informative)

Examples of Realizations

2-A.1Repeater

Two fundamental repeater structures are realizable:

The remotely controlled and the self-controlled repeater. For the remotely con-

trolled repeater in the ground state there is a preferred direction of the sig-

nal transfer: it shall always point from the upmost line to the lines beneath.

If a station or a line beneath sends a message then it shall reverse the direc-

tion of the signal transfer of the repeater before the beginning of the trans-

mission and thereafter restore the original condition. In general this means

that each line beneath needs in addition a control bus line (CNTR: control; wire

pair). The circuit expense of the repeater totals three receiver (R) and three

transmitter (T) devices (see Fig. below).

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

! Station !

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

Bus !

Line 1 ------------+------------------------------+------+------

! !

! ^CNTR +-----+-----+

+------------!-------------------!----+ ! Station !

! +-------+-------+ RS-485 ! ! +-----------+

! ! ! ! !

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

! ! + R + + + + + !

! ! + + +-----+ T + + T + !

Pre- ! + ! +--+--+ +--+--+ !

ferred ! ! ! ! TTL ! !

Direc- ! ! +-<-----!------<----+ ! Repeater

tion ! ! ! ! ! !

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

! ! + T o-----+ + + + + !

! ! + + + R + + R + !

V ! + +--+--+ +--+--+ !

! ! ! ! !

! +-------+-------+ RS-485 ! !

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

! ^CNTR

Bus ! !

Line 2 ----+-------+-------------------!-----------+-----------

! ! !

RTS Bus - - ! - + - - - - - - - - - - - + - - - - - ! - + - - -

! ^CNTR ! ^CNTR

! ! ! !

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

! Station ! ! Station !

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

Figure 2-A.1 Remotely Controlled Repeater

Page 40

PROFIBUS-Specification-Normative-Parts-2:1997

For the self-controlled repeater in the ground state both bus lines are receiv-

ers. A signal transfer happens only upon arrival of a start bit edge in the cor-

responding direction. A priority circuit resolves conflicts if a start bit edge

is received simultaneously from both sides. The detection of the end of a frame

and then the reset into the ground state is carried out by a signal idle time

watchdog (idle binary "1") of ≥ 11 bits. The circuit expense of the repeater

comprises two receiver and transmitter devices each and one direction control

with priority and idle time control (see Fig. below). The idle time control

depends on the data signalling rate, and is set to be ≥ 11

.

t

Bit

.

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

! Station !

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

Bus !

Line 1 -----------------+--------------------------+-----+------

! !

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

+-----------------!-----------------+ ! Station !

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

! ! ! RS-485 ! !

! ! + +--+--+ !

! ! + + + R + !

! ! + T +----<-----+ + + !

v ! +--+--+ +-----+-----+ + !

Basic ! ! ! Direction ! ! !

Direc- ! +-->---+ Control +---<--+ ! Repeater

tion ! ! ! (TTL) ! ! !

^ ! + +-----+-----+ +--+--+ !

! ! + + +----->----+ T + !

! ! + R + + + !

! ! +--+--+ + !

! ! ! RS-485 ! !

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

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

!

Bus !

Line 2 ------+----------+------------------------------+--------

! !

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

! Station ! ! Station !

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

Figure 2-A.2 Self-Controlled Repeater

A temporal regeneration of the bit phases is not provided for either repeater

version. Therefore the maximum number of successive repeaters is limited to

three.

2-A.2Structures of PROFIBUS Controllers

The PROFIBUS Controller (PBC) establishes the connection of a field automation

unit (control or central processing station) or a field device to the transmis-

sion medium. The PBC consists of the line transmitter/receiver (Transceiver),

the frame character transmitter/receiver (UART) and the FDL/APP processor with

the interface to the PROFIBUS user. An electrical isolation may be inserted

between the RS-485 transceiver and the UART with optical couplers as well as

with other transmission techniques between the transmission medium and trans-

ceiver, e.g. with transmitters (see Fig. below).

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