Спецификация протокола Profibus
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Table 2. Operating Parameters
+---------+-----------------------------------------------------+
! Ser. No ! Name !
+---------+-----------------------------------------------------+
! 1 ! Station Address TS !
! 2 ! Data Signalling Rate (Baud_rate; kbit/s) !
! 3 ! Single/Redundant Media available !
! 4 ! Release of Hardware and Software !
! 5 ! Slot Time T
SL
!
! 6 ! Station Delay Time min T
SDR
!
! 7 *) ! Station Delay Time max T
SDR
!
! 8 *) ! Transmitter fall/Repeater switch Time T
QUI
!
! 9 *) ! Setup Time T
SET
!
! 10 *) ! Target Rotation Time T
TR
!
! 11 *) ! GAP Update Factor G !
! 12 *) ! Master Station enter/leave the Logical Ring !
! 13 *) ! Highest Station Address (HSA) !
! 14 *) ! Maximum Number of Retries (max_retry_limit) !
+---------+-----------------------------------------------------+
! *) applies only to Master Stations !
+---------------------------------------------------------------+
4.1.7 Timer Operation
The following times T are measured in bits. A time t in seconds (s) shall there-
fore be divided by the bit time t
BIT
.
Bit Time t
BIT
:
The Bit Time t
BIT
is the time which elapses during the transmission of one bit.
It is equivalent to the reciprocal value of the transmission rate:
t
BIT
= 1 / Transmission Rate in bit/s. (2)
Syn Time T
SYN
:
The Synchronization Time T
SYN
is the minimum time interval during which each
station shall receive idle state (idle = binary "1") from the transmission
medium before it may accept the beginning of an action frame (request or send/
request frame) or token frame. The Syn Time equals:
T
SYN
= 33 bit (3)
Syn Interval Time T
SYNI
:
The Synchronization Interval Time T
SYNI
serves the supervision of the maximum
allowed time interval between two consecutive Syn Times or receiver synchroniza-
tions. This time comprises two complete message cycles, each of which consists
of two frames of maximum length and the related Syn Times. A transmission dis-
turbance is permitted in one of those Syn Times:
T
SYNI
=
2
.
(2
.
(33 bit + 255
.
11 bit)) + 33 bit = 11 385 bit (4)
Station Delay Time T
SDx
:
The Station Delay Time T
SDx
is the period of time which may elapse between the
transmission or receipt of a frame's last bit until the transmission or receipt
of a following frame's first bit (with respect to the transmission medium, i.e.
including line receiver and transmitter). The following three station delays are
defined:
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1) Station Delay of Initiator (station transmitting action or token frame):
T
SDI
= t
SDI
/ t
BIT
(5)
2) Minimum Station Delay of Responders (stations which acknowledge or respond):
min T
SDR
= min t
SDR
/ t
BIT
(6)
3) Maximum Station Delay of Responders:
max T
SDR
= max t
SDR
/ t
BIT
(7)
When transposing the NRZ signals into a different signal coding, the transmitter
fall time after switching off the transmitter (at the initiator) shall be taken
into account if it is greater than T
SDR
. During this Quiet Time T
QUI
transmis-
sion and receipt of frames shall be disabled. This shall also be taken into ac-
count when using self-controlled repeaters, whose switching time shall be taken
into consideration. For T
QUI
:
T
QUI
< min T
SDR
(8)
In order to fulfil condition (8), it may be necessary to prolong T
SDR
.
Ready Time T
RDY
:
The Ready Time T
RDY
is the time within which a master station shall be ready to
receive an acknowledgement or response after transmitting a request. The Ready
Time is defined as follows:
T
RDY
< min T
SDR
(9)
In order to fulfil this condition it may be necessary to prolong T
SDR
.
When transposing NRZ signals into a different signal coding, the Quiet Time
shall also be taken into consideration when switching off the transmitter. The
receiver shall not be enabled before this time:
T
QUI
< T
RDY
(10)
In order to fulfil this condition, it may be necessary to prolong T
RDY
and thus
T
SDR
accordingly.
Safety Margin T
SM
:
The following time interval is defined as Safety Margin T
SM
:
T
SM
= 2 bit + 2
.
T
SET
+ T
QUI
(11)
T
SET
is the set-up time which expires from the occurrence of an event (e.g.
interrupt: last octet sent or Syn Time expired) until the necessary reac-
tion is performed (e.g. to start Syn Time or to enable the receiver):
T
SET
= t
SET
/ t
BIT
(12)
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Idle Time T
ID
:
The Idle Time T
ID
is the time which expires at the initiator after receipt of a
frame's last bit (measured at the line receiver) as idle = binary "1" on the
transmission medium, until a new frame's first bit is transmitted on the medium
(including line transmitter). The Idle Time is also the time which expires be-
tween transmitting the last bit of a frame which is not to be acknowledged and
transmitting the first bit of the next frame. The Idle Time shall be least the
Syn Time plus the Safety Margin T
SM
(see Fig. 3 and Fig. 4, case a)). At high
transmission rates (see Fig. 3 and Fig. 4, case b)and c)) the Syn Time is very
short, hence the station delays become significant and shall be taken into con-
sideration. Two Idle Times are distinguished. After an acknowledgement, response
or token frame the Idle Time is defined as follows:
Ack./Res./Token
Responder:
+=============+
!
!
! T
ID1
Send/Req./Token
Initiator:
+=============+
------------------->
+===============+
a) +-:-:>- - ->---->:::>
minT
SDR
<T
SDI
<(T
SYN
+T
SM
)
or b) +---->:::>-:-:>- - ->
(T
SYN
+T
SM
)<minT
SDR
<T
SDI
or c) +---->:::>- - ->-:-:>
(T
SYN
+T
SM
)<T
SDI
<minT
SDR
T
ID1
= max
(
T
SYN
+ T
SM
, min T
SDR
, T
SDI
)
*)
(13)
*) the maximum of the three values.
Figure 3. Idle Time T
ID1
The parameter min T
SDR
is extreme short to define because of the dynamic of the
system, but to select greater than the Ready Time T
RDY
. If the necessary delay
time cannot be reached with the range of value of T
SET
, than the min T
SDR
shall
be made longer.
After an action frame, which is not to be acknowledged (Send Data with No
Acknowledge, SDN) the Idle Time is defined as:
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SDN T
ID2
Send/Req./Token
Initiator:
+=============+
------------------->
+===============+
a) +- - - ->------>::::>
! max T
SDR
< (T
SYN
+T
SM
) !
or b) +------>::::>- - - ->
! (T
SYN
+T
SM
) < max T
SDR
!
! a) max T
SDR
!
Receiver:
+=============+
- - - ->- - - - - ->
+===============+
or b) max T
SDR
T
ID2
= max
(
T
SYN
+ T
SM
, max T
SDR
)
*)
(14)
*) the maximum of the two values.
Figure 4. Idle Time T
ID2
Transmission Delay Time T
TD
:
The Transmission Delay Time T
TD
is the maximum time which elapses on the trans-
mission 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
TD
= t
TD
/ t
BIT
(15)
e.g. given a line length of 200 m without repeaters, t
TD
is approx. 1 µs and
thus at 500 kbit/s T
TD
= 0,5 bit.
Slot Time T
SL
:
The Slot Time T
SL
is the maximum time the initiator waits for the complete
receipt of the first frame character (see subclause 4.5.1, UART Character, 1 UC
= 11 bits) of the immediate acknowledgement or response, after transmitting the
last bit of an action frame (including the line transmitter). Furthermore, T
SL
is the maximum time the initiator waits for the token receiver's first frame
character after transmitting a token frame. Theoretically two Slot Times are
distinguished. After an action frame (request or send/request) the Slot Time is
calculated as follows:
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T
SL1
+----------------------------->
::::> T
SM
Send/Req. 1.UC
Initiator:
+===========+
+====+==============+
! !
! !
T
TD
T
TD
! !
! !
Responder:
+===========+
- - - - - ->
+====+==============+
max T
SDR
Ack./Res.
T
SL1
= 2
.
T
TD
+ max T
SDR
+ 11 bit + T
SM
(16)
Figure 5. Slot Time T
SL1
After a token frame the Slot Time is calculated as follows:
T
SL2
+--------------------------------->
::::> T
SM
Token 1.UC
Initiator:
+=======+
----->
+====+==============+
! T
SYN
!
! !
T
TD
T
TD
! !
! !
Responder:
+=======+
- - - - - - - ->
+====+==============+
max T
ID1
Send/Req./Token
T
SL2
= 2
.
T
TD
+ max T
ID1
+ 11 bit + T
SM
(17)
Figure 6. Slot Time T
SL2
In order to simplify the realization, only
one
Slot Time, the longer one, is
used in the system. This does not influence the system reaction time negatively,
as the Slot Time is a pure monitoring time.
T
SL
= max
(
T
SL1
, T
SL2
)
*)
(18)
*) the larger value shall be chosen
Time-out T
TO
:
The time-out T
TO
serves to monitor the master and slave station's bus activity
and Idle Time. Monitoring starts after PON, immediately in the "Listen_Token" or
"Passive_Idle" state or later after receiving the last bit of a frame. It ends
after receiving the first bit of a following frame. If the Idle Time reaches
time-out, the bus is regarded as inactive (error, e.g. due to lost token). The
time-out is defined as follows:
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T
TO
= 6
.
T
SL
+ 2
.
n
.
T
SL
(19)
For master stations: n = station address (0 to 126)
For slave stations: n = 130, independent of its station address
The first term makes sure that there is sufficient difference to the maximum
possible Idle Time between two frames. The second term ensures that not all
master stations claim the token at the same moment after an error has occurred.
GAP Update Time T
GUD
:
The GAP Update Time T
GUD
serves the master station for initializing GAP mainte-
nance. After the first generation of the GAPL, updating the GAP image is cycli-
cally initialized after every interval T
GUD
. This initialization takes place at
the next possible token receipt, if there is still Token Holding Time available
after the regular message cycles, or during later token holding phases. The GAP
Update Time is a multiple of the Target Rotation Time T
TR
and is defined as fol-
lows:
T
GUD
= G
.
T
TR
1 ≤ G ≤ 100 (20)
T
TR
is the predefined Target Rotation Time (see subclause 4.1.1.4).
4.2 Cycle and System Reaction Times
4.2.1 Token Cycle Time
The base load in a system with several master stations, i.e. the bus load caused
by medium access control (token frames) and not by regular message cycles, is
determined by the Token Cycle TC. The total base load per token rotation results
from na (number of master stations) token cycles. The cycle time T
TC
is composed
of the Token Frame Time T
TF
, the Transmission Delay Time T
TD
and the Idle Time
T
ID
. T
ID
results from the Station Delay Time T
SD
or the Syn Time T
SYN
respec-
tively. T
TC
is measured in bits:
Master +-----------+
Station k ! Token k !------+
+-----------+ !
T
TF
T
TD
!
!
T
ID
!
Master ! +-----------+
Station k+1 +----->! Token k+1 !--------+
+-----------+ !
(or Send/Req.) !
!
Token Cycle Time T
TC
V
+<----------------------->+
T
TC
= T
TF
+ T
TD
+ T
ID
(21)
Figure 7. Token Cycle
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The Token Frame Time T
TF
is determined by the number of frame characters UC
(UART character). A frame character always consists of 11 bits (see subclause
4.5.1) and hence the token frame comprises altogether 33 bits. The Transmission
Delay Time T
TD
depends on the line length (about 5 ns/m without repeater) and is
mostly substantially less than the other times. The Idle Time T
ID
, which elapses
between the token frames, contains the Station Delay Time T
SDI
of the token
receiver on the one hand, on the other hand the Syn Time T
SYN
+ T
SM
shall be
used, if this sum is larger than T
SDI
(see subclause 4.1.7). This mainly occurs
at low transmission rates (< 100 kbit/s).
4.2.2 Message Cycle Time
A message cycle MC consists of the action frame (request or send/request frame)
and the reply frame (acknowledgement or response frame). The cycle time is com-
posed of the frame transmission times, the transmission delay times and the sta-
tion delay times.
The Station Delay Time T
SDR
elapses between request and acknowledgement or
response. This time is needed for decoding the request and assembling the
acknowledgement or response frame. It depends on the protocol implementation in
the station and is mostly substantially greater than the Transmission Delay Time
T
TD
. The Idle Time T
ID
, which elapses between acknowledgement or response and
new request, contains also the Station Delay Time (see subclause 4.1.7).
However, T
SYN
+ T
SM
shall be used, if this sum is greater than T
SDI
.
Master +----------+ +----------+
Station ! Send/Req.!--+ +-->! Send/Req.!
+----------+ ! ! +----------+
T
S/R
T
TD
! ! (or Token)
! !
T
SDR
T
ID
! !
! +----------------+ !
Master/Slave +--->! Ack./Response !---+
Station +----------------+
T
A/R
T
TD
Message Cycle Time T
MC
+<----------------------------------------->+
T
MC
= T
S/R
+ T
SDR
+ T
A/R
+ T
ID
+ 2
.
T
TD
(22)
Figure 8. Message Cycle
At transmission rates < 100 kbit/s decoding and evaluation of frames may par-
tially keep pace with their reception. Station delay times become considerably
shorter then.
The frame transmission times (T
S/R
, T
A/R
) are determined by the number of frame
characters (UC). Thus they are calculated as follows:
T
S/R
= a
.
11 bit a No. of UC in Send/Request Frame
T
A/R
= b
.
11 bit b No. of UC in Ack./Response Frame
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EXAMPLE:
a = 6 for the request frame:
T
S/R
= 66 bit
b = 59 for the response frame (50 octet DATA_UNIT):
T
A/R
= 649 bit
4.2.3 System Reaction Times
The message rate R
SYS
in the system equals the possible number of message cycles
per second:
R
SYS
= 1 / t
MC
;t
MC
= T
MC
.
t
BIT
(23)
The maximum system reaction time T
SR
in a system with one master station and n
slave stations (master slave system) in pure polling mode is calculated from the
message cycle time and the number of slave stations. If message retries are al-
lowed for, T
SR
is calculated as follows:
T
SR
= np
.
T
MC
+ mp
.
RET T
MC
(24)
where:
np number of slave stations
mp number of message retry cycles per Poll Cycle
RET T
MC
message retry cycle time
The maximum System Reaction Time in a system with several master stations and
slave stations equals the Target Rotation Time:
T
SR
= T
TR
(see subclause 4.1.1.4) (25)
4.3 Error Control Procedures
Line protocol errors, such as e.g. frame errors, overrun errors and parity er-
rors, and transmission protocol errors, such as e.g. faulty start delimiters,
frame check octets and end delimiters, invalid frame length, response times,
etc., result in the following station reactions:
An action frame (request, send/request or token) that has been received incor-
rectly by a station shall not be processed, acknowledged or answered. The in-
itiator shall retry the request after expiration of the Slot Time. The request
shall also be retried if the acknowledgement or response was corrupted. The in-
itiator shall complete a request only after having received a valid response or
if the retry (retries) was not (were not) successful (see subclause 4.1.6,
operating parameters). This means that a "Send/Request" shall be kept until the
responder confirms
its correct receipt by an acknowledgement or response or the retry (retries) was
not (were not) successful. In the same way, a responder shall terminate a
"Request" or "Send/Request" only if a new request with altered Frame Count Bit
is received or another station is addressed (see subclause 4.7.3, FCB).
If a station does not acknowledge or respond in cyclic or acyclic mode after re-
try (retries), it is marked as "non operational". When processing the following
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requests, the initiator transmits the request to this station without retry
(retries), until the station acknowledges or responds correctly again. After
positive acknowledgement the initiator marks again the addressed station as
"operational". When processing the next request, the initiator continues the
original mode of operation with this station.
4.4 Timers and Counters
In order to measure the token rotation time and to realize the supervisory times
the following timers are necessary:
Token Rotation Timer, Idle Timer, Slot Timer, Time-out Timer, Syn Interval Timer
and GAP Update Timer.
Token Rotation Timer: When a master station receives the token, this timer is
loaded with the Target Rotation Time T
TR
and decremented each bit time. When the
station again receives the token, the timer value, the remaining time or Token
Holding Time T
TH
, is read and the timer reloaded with T
TR
. The Real Rotation
Time T
RR
results from the difference T
TR
- T
TH
. Low priority message cycles may
be processed if at the instant of processing T
RR
< T
TR
.
Idle Timer: This timer monitors the idle state (binary "1"), the Syn Time, imme-
diately on the bus line. The Syn Time preceding each request is necessary for
unambiguous receiver synchronization. The Idle Timer of slave stations and
master stations "without token" is loaded with T
SYN
after the transmission or
receipt of a frame's last bit and then decremented each bit time. The receiver
shall be enabled immediately after the timer has expired. The timer of a master
station "with token" is loaded according to the data transmission service with
T
ID1
or T
ID2
(see subclause 4.1.7). A new request or token frame may only be
transmitted after expiration of the timer. When the signalling level is binary
"0", the timer is always reloaded.
Slot Timer: This timer in a master station monitors after a request or token
pass whether the receiving station responds or becomes active within the prede-
fined time T
SL
, the Slot Time. After transmission of a frame's last bit this
timer is loaded with T
SL
and decremented each bit time as soon as the receiver
is enabled. If the timer expires before a frame's first bit is received, an er-
ror has occurred. Then a retry or a new message cycle is initiated.
Time-out Timer: This timer monitors bus activity in master and slave stations.
After the transmission or receipt of a frame's last bit the timer is loaded with
a multiple of the Slot Time (see subclause 4.1.7) and decremented each bit time
as long as no new frame is received. If the timer expires, a fatal error has
occurred, which for the master station causes a (re)initialization. The FMA1/2
User of the slave and master station receives a time-out notification (see
Part 3, subclause 4.2.3.3).
Syn Interval Timer: Master and slave stations use this timer to monitor the
transmission medium as to whether a receiver synchronizing (T
SYN
, idle state,
idle = binary "1") occurs within T
SYNI
. Each time the receiver is synchronized,
the timer is loaded with T
SYNI
(see subclause 4.1.7). From the beginning of a
frame (first start bit) the timer is decremented each bit time as long as no new
T
SYN
is detected. If the timer expires, an error has occurred on the
transmission medium, e.g. stuck at "0" or permanent "0" / "1" edges. The FMA1/2
User is notified accordingly (see Part 3, subclause 4.2.3.3).
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GAP Update Timer: Only master stations need this timer. Its expiration indicates
the moment for GAP maintenance. After a complete GAP check, which may last sev-
eral token rotations (segmented; see subclause 4.1.1.2), the timer is loaded
with a multiple of the Target Rotation Time T
TR
(see subclause 4.1.7).
When a master station enters the "Listen_Token" state, the Idle Timer is loaded
with T
SYN
, the Time-out Timer with T
TO
, the Syn Interval Timer with T
SYNI
and
the other timers are cleared. When a slave station enters the "Passive_Idle"
state, the Time-out Timer is loaded with T
TO
and the Syn Interval Timer with
T
SYNI
.
For installation and maintenance the following counters (FDL variables) are
optionally defined in pairs:
For master stations:
- counter for transmitted frames (Frame_sent_count for Request frames) except
for SDN service and FDL status
- counter for transmitted frame retries (Retry_count)
For slave and master stations:
- counter for received valid start delimiters (SD_count)
- counter for received invalid start delimiters (SD_error_count)
When a station enters the "Listen_Token" or "Passive_Idle" state, the counters
are cleared and enabled. If a counter reaches its maximum (see Part 3, subclause
5.2.3.2, table "Additional FDL Variables"), counting of this counter as well as
of the related comparative counter is stopped. When clearing a counter the
related comparative counter is also cleared and they are enabled again. The
FMA1/2 user may access these counters using the Set/Read Value FMA1/2 services
(see Part 3, clause 4.2).
In relation to stations multiple counters (statistics) are possible (optional,
see part 8).