Спецификация протокола Profibus

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6 Scope

The part of the specification is based on the architectural model, the bus

access protocol and the transmission procedures as described in the PROFIBUS

Specification "Data Link Layer".

The data transmission technique of Layer 1 (Physical Layer, PhL) is based on the

rules defined in IEC 1158-2, clause 11.

The frame format builds on the synchronous Protocol Data Unit (Ph-PDU) described

in clause 9 of IEC 1158-2. It consist of a Preamble, a Start Delimiter and an

End Delimiter as well as the Layer 2 data (FDL-PDU). The data are coded and

decoded according to the Manchester-Biphase-L-Code.

The transmission protocol of Layer 2 as well as the Layer 1 management (FMA1)

are defined according to IEC 1158-2, clauses 5 and 6.

Appendix A explains possible structures for repeaters, fieldbus interfaces and

systems with several fieldbus lines connected to a single master station.

Guidelines on a redundant central control unit and a bus analyzer/diagnostic

unit are added, too. Finally, the number of connectable stations for intrinsic

safe fieldbus with power supply over the bus as well as the data transfer rate

and the system reaction time are calculated for an example under consideration

of the frame formats that have been changed by the integration of IEC 1158-2.

7 Data Transmission (Physical Medium, Physical Layer)

7.1 Electrical Characteristics

The Physical Layer described in IEC 1158-2 clause 11 shall be used.

Version 1: 31.25 kbit/s, voltage mode and wire medium (intrinsically safe

Physical Layer)

Repeater

An extension of line length and an increase in the number of stations may be

achieved by means of bi-directional amplifiers (called repeaters, see clause A.1

of this part). The maximum number of repeaters between two stations is four. The

following maximum values shall apply for 31.25 kbit/s and if the bus segments

are in series (linear bus topology):

- 31.25 kbit/s:

1 Repeater: 3.8 km and 62 stations

2 Repeater: 5.7 km and 92 stations (see figure 2)

3 Repeater: 7.6 km and 122 stations

4 Repeater: 9.5 km and 127 stations

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M/S M/S M/S

REP

M/S M/SM/S

REP

Section 1 maximum 31 Stations + 1 Repeater

Section 3 maximum 31 Stations + 1 Repeater

Section 2 maximum 30 Stations + 2 Repeaters

M/S Master/Slave Station

REP Repeater

Bus Terminator

Figure 2: Repeater in Linear Bus Topology (cf Fig. 2 of Part 2)

For a tree topology of segments the following maximum values shall apply at

31.25 kbit/s:

e.g.. 5 Repeaters: 7.6 km and 127 stations

M/S

REP

Section 1

Section 3

Section 4

Section 2

max. 31 Stn

Section 5

max. 30 Stn

max. 28 Stn

max. 31 Stn

M/S

REP

Section 6

max. 31 Stn

M/S Master/Slave Station

REP Repeater

Bus Terminator

Stn Stations

Total number of

Stations on all

Sections: 127

Figure 3: Repeater in Tree Topology (cf Fig. 3 of Part 2)

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7.2 Interface between Physical Layer (PhL) and Medium Access and Transmission

Protocol (FDL)

This clause gives an abstract definition of the Ph-Data service that is provided

to the FDL-Layer by the Physical Layer. The Ph-Data service is for the receipt

and transmission of data (one octet at a time).

The execution of the interface and the control within a station are not fixed or

stipulated.

The following service primitives have been taken unchanged from IEC 1158-2 and

have been repeated for clarity.

Ph-DATA request (class, data)

Ph-DATA indication (class, data)

Ph-DATA confirmation (status)

The parameter class specifies the Physical Layer Interface Control Information

(PhICI) of the Physical Layer Interface Data Unit (PhIDU). The following values

are possible for the Ph-Data request primitive:

a) START-OF-ACTIVITY

b) DATA

c) END-OF-DATA-AND-ACTIVITY

For the Ph-DATA indication primitive the parameter class contains the following

values:

a) START-OF-ACTIVITY

b) DATA

c) END-OF-DATA

d) END-OF-ACTIVITY

e) END-OF-DATA-AND-ACTIVITY

They are available to the interface between physical medium and medium access

control protocol and transmission protocol.

The parameter data specifies the Physical Layer Interface Data (PhID) of the

Physical Layer Interface Data Unit (PhIDU). It consists of an octet Physical

Layer User Data which has to be sent (request) or received (indication).

The parameter status marks either the success or a detected failure of the

transmission.

The Ph-DATA confirm primitive marks the end of a transmission. It is passed on

to the FDL-controller after a transmission has been completed and it indicates

thereby the Physical Layer’s readiness to receive the next Ph-Data request

primitive.

The Physical Layer Data service with primitives as well as the definition of the

parameter values are described in IEC 1158-2, clause 5.

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7.3 Redundancy of Physical Layer and Medium (optional)

To increase the reliability, a redundant transmission line is allowed by

PROFIBUS "Data Transmission". Its configuration shall conform to the specifica-

tions stipulated in IEC 1158-2, subclause 11.2.2, rule 9.

In principle, the telegrams have to be sent simultaneously by several

transmitters (usually more than two). A receiver is selected upon each

reception. The parameter setting of the transmitter channels and the receiver

channels is carried out by means of the Ph-SETVALUE request via the Physical

Management Interface.

The selection of the appropriate receiver channel is carried out by Layer 2

(FDL) by watching over activity on the transmission lines independently of other

stations. As described in Part 2, subclause 4.3, the following main criteria

apply for switching from a given receiver channel:

- Two or more invalid frames are received in succession.

Invalid means: invalid format and invalid CRC.

- Time-out T

expired, see subclause 8.1.7 of this part.

- No Syn Time T

SYN

was notified during a Synchronization Interval Time T

SYNI

see subclause 8.1.7 of this part.

Dependent on the execution, further switch conditions may be selected.

8 Medium Access Methods and Transmission Protocol (Data Link Layer, FDL)

The medium access method and the transmission protocol (Data Link Layer, FDL),

which are described in the PROFIBUS Specification "Medium Access Methods" and

"Transmission Protocol", shall apply for this part, except for the deviations

specified in the following corresponding subclauses. Due to the extensions to

the frame formats (IEC 1158-2 synchronous transmission protocol), the timer

calculations have to be modified in part as described in subclause 8.1.7 of this

part.

8.1 Transmission Procedures and FDL Controller

8.1.1 Token Procedures

The specifications of subclause 4.1.1 of Part 4 shall apply.

8.1.1.1 Token Passing

The specifications of subclause 4.1.1.1 of Part 4 shall apply .

8.1.1.2 Addition and Removal of Stations

The specifications of subclause 4.1.1.2 of Part 4 shall apply

8.1.1.3 (Re)Initialization the Logical Token Ring

The specifications of subclause 4.1.1.3 of Part 4 shall apply

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8.1.1.4 Token Rotation Time

The specifications of subclause 4.1.1.4 of Part 4 shall apply.

8.1.1.5 Message Priorities

The specifications of subclause 4.1.1.5 of Part 4 shall apply.

8.1.2 Acyclic Request or Send / Request Mode

The specifications of subclause 4.1.2 of Part 4 shall apply.

8.1.3 Cyclic Send / Request Mode

The specifications of subclause 4.1.3 of Part 4 shall apply.

8.1.4 Request FDL Status of all Stations (Live List)

The specifications of subclause 4.1.4 of Part 4 shall apply.

8.1.5 Status of the FDL Controller

The specifications of subclause 4.1.5 of Part 4 shall apply.

8.1.6 FDL Initialization

The specifications of subclause 4.1.6 of Part 4 shall apply for FDL

initialization. Because of the different Ph Layer complying to IEC 1158-2, the

operational parameter T

QUI

(Transmitter fall Time / Repeater switch time) shall

be renamed post-transmission gap.

8.1.7 Timer Operation

The following times T are measured in bits as in the PROFIBUS Specification

"Medium Access Methods" and "Transmission Protocol". A time t in seconds (s)

shall therefore be divided by the Bit Time t

BIT

Bit-Time t

BIT:

The Bit Time

bit

is the time which elapses during the transmission of one bit.

It is equivalent to the reciprocal value of the transmission rate:

BIT

=1 / Transmission Rate (bit/s) (1)

Syn Time T

SYN

The minimum time interval during which each station shall receive no activity

from the transmission medium before it may accept the begin of a request

(request or send/request) or token frame.

The Syn Time corresponds to the post-transmission gap time that is defined in

IEC 1158-2, clause 9. It is at least 4 bit and may be increased by FMA1/2 up to

32 bit.

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SYN

= T

PTG

= Post-transmission Gap Time = T

QUI

SYN

= 4 to 32 bit (2)

Ack./Res./Token Send/Req./Token

+===============+---------->+===============+

SYN

PTG

QUI

Figure 4: Syn-Time T

SYN

Syn Interval Time T

SYNI

The Synchronization Interval Time T

SYNI

serves to monitor the maximum allowed

time interval between two consecutive receptions of Ph-DATA indication

primitives of the classes: START-OF-ACTIVITY and END-OF-ACTIVITY (or END-OF-

DATA-AND-ACTIVITY), in order to detect "permanent transmitters".

This time comprises two complete message sequences, each of which consists of

two PDUs of maximum length and the associated maximum Physical Layer Control

Information (PhPCI: Preamble, Start Delimiter, End Delimiter) and the maximum

Syn Time (post-transmission gap).

Three Ph-Data indications of class END-OF-ACTIVITY (or END-OF-DATA-AND-ACTIVITY)

may fail thereby.

SYNI

= 2 · ( 2 · (T

SYN

+ Ph

PCI

+ T

FDL

)) +64

(3)

The constant 64 constitutes a safety margin.

FDL

= maximum length of a FDL frame (see clauses 8.5 and 8.6 of this part)

SYNI

= 2 · ( 2 · (32 + 80 + 255 · 8))+64 = 8 672 bit (4)

Station Delay Time T

SDx

The Station Delay Time T

SDX

is the period of time which may elapse between a Ph-

DATA request primitive (class: END-OF-DATA-AND-ACTIVITY) or Ph-DATA indication

primitive (class: END-OF-ACTIVITY or END-OF-DATA-AND-ACTIVITY) until the

following Ph-DATA request primitive (class: START-OF-ACTIVITY) or a Ph-DATA

indication primitive (class: START-OF-ACTIVITY) (relative to the transmission

medium, i.e. including the Physical Layer Entity).

The following three station delays are defined:

1) Station Delay of Initiator (station transmitting request or token frame)

SDI

= t

SDI

/ t

BIT

(5)

2) Minimum Station Delay of Responders (station that acknowledges or responds)

min T

SDR

= min t

SDR

/ t

BIT

(6)

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3) Maximum Station Delay of Responders

max T

SDR

= max t

SDR

/ t

BIT

(7)

Quiet Time T

QUI

= T

PTG

The Transmitter Fall Time or Repeater Switch Time corresponds to the Post-

transmission Gap Time (T

SYN

). The following shall apply:

QUI

= T

PTG

= T

SYN

(8)

Ready Time T

RDY

The Ready Time T

RDY

is the time within which a master station shall be ready to

receive an acknowledgment or response after transmitting a request. The Ready

Time is defined as follows:

RDY

< min T

SDR

(9)

In order to fulfill this condition it may be necessary to prolong T

SDR

While disconnecting the transmitter the Quiet Time shall be considered. The

readiness may start only after this time:

QUI

= T

PTG

= T

SYN

< T

RDY

(10)

In order to fulfill this condition the T

SDR

shall be increased according to

equation (9) if necessary.

Safety Margin T

The following time interval is defined as Safety Margin T

= 2 bit + 2 · T

SET

(11)

SET

is the set-up time which expires from the occurrence of an event

(e.g. Ph-Data confirm) until the execution of the necessary reaction:

SET

= t

SET

/ t

BIT

(12)

Idle Time T

The Idle Time T

is the time which expires at the initiator after a Ph-DATA

indication primitive (class: END-OF-ACTIVITY or END-OF-DATA-AND-ACTIVITY) until

reception of a new frame with Ph-DATA request primitive (class: START-OF-

ACTIVITY) or after passing a Ph-DATA request primitive (class: END-OF-DATA-AND-

ACTIVITY) with a Ph-DATA confirm primitive to transmit a frame which is not to

be acknowledged until passing a new Ph-DATA request primitive (class: START-OF-

ACTIVITY) for transmitting the next frame. The Idle Time shall be at least the

Syn Time plus the Safety Margin T

(see description of Idle Time in subclause

4.1.7 of Part 4).

After an acknowledgment, response or token frame the Idle Time is defined as

follows:

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Ack./Res./Token

Responder: +=============+

! Send/Req./Token

Initiator: +=============+-------------------->+============+

a) +-:-:->- - ->----->::::>

min T

SDR

SDI

<(T

SYN

)

or b) +----->::::>-:-:->- - ->

SYN

)<min T

SDR

SDI

or c) +----->::::>- - ->-:-:->

SYN

)<T

SDI

<min T

SDR

ID1

= max (T

SYN

+ T

, min T

SDR

, T

SDI

) (13)

(The maximum value shall be used in each case)

Figure 5: Idle Time T

ID1

(cf Fig. 3 of Part 4)

After a request frame, which is not to be acknowledged, the following Idle Time

shall apply (cf also Fig. 4 of Part 4):

ID2

= max (T

SYN

+ T

, max T

SDR

) (14)

(The maximum value shall be used in each case)

Transmission Delay Time T

The Transmission Delay Time T

is the maximum time which elapses on the

transmission medium between transmitter and receiver when a frame is

transmitted. Delay times of repeaters shall be considered if necessary. The

Transmission Delay Time is defined as follows:

= t

/ t

BIT

(15)

Compliant to IEC 1158-2, clause 11, rule 4, the value of 20 bit times shall not

be surpassed.

Slot Time T

The Slot Time T

is the maximum time the initiator waits after passing a Ph-

DATA request primitive (class: END-OF-DATA-AND-ACTIVITY) for transmitting a

request frame from the Ph-DATA confirm primitive until receiving the first Ph-

DATA indication primitive (class: DATA) as an indication of receiving the

immediate acknowledgment or answer. Furthermore, T

is the maximum time the

initiator waits for a Ph-DATA indication primitive (class: DATA) after the token

frame as reaction to receiving a frame from the token receiver. Theoretically

two Slot Times are distinguished (see description of Slot Time in subclause

4.1.7 of the Part 4, Fig. 5 and Fig. 6). After a request frame (request or

send/request) the following Slot Time shall apply:

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SL1

= 2 · T

+ max T

SDR

+ T

PRE

+ 16 bit + T

(16)

After a token frame the following Slot Time shall apply:

SL2

= 2 · T

+ max T

ID1

+ T

PRE

+ 16 bit + T

(17)

PRE

: Preamble period (see IEC 1158-2)

Note: In order to simplify the realization, only the longer Slot Time is used in

the system. This does not influence the system reaction time negatively,

as the Slot Time is merely a monitoring time.

= max (T

SL1

, T

SL2

) (18)

(The maximum value shall be used in each case)

Time-out T

The time-out T

serves to monitor the master and slave stations’ line activity

and Idle Time. Monitoring starts either immediately after the PON, in the

"Listen_Token" or "Passive_Idle" state or later after the reception of a Ph-

DATA indication primitive (class: END-OF-ACTIVITY or END-OF-DATA-AND-ACTIVITY).

It finishes upon receipt of a Ph-DATA indication primitive (class: START-OF-

ACTIVITY) for reception of a following frame. If the Idle Time reaches the Time-

out value, the bus is regarded as inactive (error case, e.g. due to lost token).

The Time-out is defined as follows (cf also Part 4, subclause 4.1.7 "Time-out"):

= 6 · T

+ 2 · n · T

(19)

For master stations: n = station address (0 to 126)

For slave stations: n = 130, independent of their station address

GAP Update Time T

GUD

The specifications of the subclause 4.1.7 of Part 4 shall apply.

8.2 Cycle and System Reaction Times

8.2.1 Token Cycle Time

Similar to PROFIBUS Specification "Medium Access Methods" and "Transmission

Protocol", the following shall apply for the Token Cycle Time T

= T

+ T

(20)

Due to the frame character (cf subclause 9.5.1 of this part) and the changed

frame format (cf subclauses 8.6 and 8.7), the Token Frame Time T

is 64 bit

with a preamble of 8 bit.

Furthermore, it shall be noted that only the transmission speed 31.25 kbit/s may

be selected.

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8.2.2 Message Cycle Time

The following shall apply for the Message Cycle Time T

= T

S/R

+ T

SDR

+ T

A/R

+ T

+ 2 · T

(21)

The specifications for the Message Cycle Time stipulated in the subclause 4.2.2

of the Part 4 shall apply except for the following cases:

The PDU transmission times (T

S/R

, T

A/R

) are determined by the number of PDU

octets.

It follows from this that:

S/R

= a · 8 bit a = number of octets in Send/Request PDU

A/R

= b · 8 bit b = number of octets in Ack/Response PDU

Example:

a = 9 for the Request PDU (1 octet Preamble):

S/R

=72 bit

b = 62 for the Response PDU ( 1 octet Preamble, 50 octet DATA_UNIT):

A/R

= 496 bit

8.2.3 System Reaction Times

The specifications for the System Reaction Times stipulated in the subclause

4.2.3 of Part 4, shall apply.

8.3 Error Control Procedures

As described in Part 4, subclause 4.3, errors in the line protocol (see IEC

1158-2, clause 9) and in the medium access protocol, such as erroneous start

octets and CRC octets, frame length, response times etc. may result in the

specified station reactions.

8.4 Timers and Counters

As explained in subclause 4.4 of Part 4, the following timers are needed to

measure the Token Rotation Time and to realize the monitor timers:

Token Rotation Timer, Idle Timer, Slot Timer, Time-out Timer, Syn Interval Timer

and GAP Update Timer.

Token Rotation Timer: The functionality of this timer is as defined in PROFIBUS

Specification "Medium Access Methods" and "Transmission Protocol".

Idle Timer: This timer monitors the idle state T

PTG

= T

SYN

= T

QUI

on the bus

line. The Idle Timer in the master station with the token is loaded with T

ID1

ID2

depending on the data transmission service (cf subclause 9.1.7 of this

part). The timer is decremented every bit time, when after a Ph-DATA request

primitive (class: END-OF-DATA-AND-ACTIVITY) either the Ph-DATA confirm primitive

at the transmitter or the Ph-DATA indication primitive (class: END-OF-ACTIVITY

or END-OF-DATA-AND-ACTIVITY) at the receiver is transferred. A new request or a

new token frame may be transmitted only after expiration of the timer.

Slot Timer: After a request from or a token transfer by a master station, this

timer of the master station monitors whether the receiving station responds or

becomes active within the defined Slot Time T

. The timer is initialized with