Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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I
TITLE OF THE INVENTION
DATA TRANSMISSION METHOD AND SYSTEM THEREFOR
BACKGROUND OF THE INVENTION
Field: of the Invention
This invention relates to a method of
transmitting data and a system therefor between a
plurality of electronic control units installed on an
automotive vehicle via a common communication line
connecting these electronic control units.
Prior Art
Conventionally, in performing mutual data
transmission between a plurality of electronic control
units (hereinafter referred to as the "ECU's")installed
on an automotive vehicle via a common communication
line (hereinafter referred to as "the network bus")
connecting the ECU's, a token passing method is
employed for circulating a transmission right round the
ECU's in a predetermined sequence to permit an ECU
having received the transmission right to send out data
to the network bus.
When a data transmission system employing the
token passing method is started, the following methods
are conventionally known for initially rendering (i.e.
generating) the transmission right to one of the ECU's:
(1) Fixed ECU method of initially rendering the
transmission right to a particular ECU determined in
advance in a f_xed manner.
(2) waiting method in which all the ECU's start
transmitting data assuming that they are each initially
rendered with the transmission right, stop transmitting
data when collision of data occurs, and restart data
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transmission after waiting for predetermined waiting
time periods set to the ECU's, respectively, repeatedly
carrying out this procedure until no collision occurs,
to thereby restrict an initial holder of the
transmission right to one of the ECU's.
However, the fixed ECU method suffers from a
problem that if the particular ECU to which the
transmission right is to be initially rendered is in
failure, the transmission right cannot be produced for
ever.
With the waiting method as well, there is an
inconvenience that it takes much time to generate the
transmission right, and time is wastefully consumed
before the ECU's start to cooperate as a network.
On the other hand, in the data transmission
system using the token passing method, it is a known
technique to add broadcast data to a message for .
transmission to transfer the transmission right to the
next ECU, as disclosed e.g. in Japanese Patent
Publication (Kokoku) No. 1-58900.
However, according to this conventional
technique, the message data format is not constructed
such that a sending end can confirm safe and accurate
transfer of each of the transmission right and data,
and hence there is room for improvement thereof to
expedite the transmission.
Further, Japanese Patent Publication (Kokoku)
No. 1-57856 (hereinafter referred to as "the first
prior art") discloses a technique that when data
transmission is not successfully carried out,
retransmission of data is performed upon the
transmission right returning to the present ECU after
having been transferred :round the ECU's, taking into
consideration the fact that if retransmission of the
data is carried out immediately, there is a high
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possibility of failure thereof.
Further, Japanese Provisional Patent Publication
(Kokai) No. 62-159539 discloses a data transmission
system (hereinafter referred to as "the second prior
art") in which when transmission of the data is not
successfully carried out, the data is retransmitted
within a limit of a predetermined number of times,
which number can be changed or set by another control
system.
According to the first prior art, the
retransmission of data is performed only after the
transmission right has been transferred round the ECU's
once even if the immediate transmission of data might
be successful (e.g. when failure of transmission was
caused by a noise during transmission), which is an
inconvenience to be eliminated for prompt completion of
data transmission.
Further, according to the second prior art, the
retransmission of data is carried out immediately after
failure thereof within the predetermined number of
times set by the other control system. However, this
number is not set by the sending end itself, and hence
it is difficult to perform prompt reaction to failure
of transmission.
Further, in making a check as to whether
connection between one member (ECU) and another (ECU)
of the network is safely established, a special message
is sent out from the one member for a response from the
other, based on which it is determined whether the
connection is safely established.
When the special message is used, however, the
data transmission and transfer of the transmission
right cannot be performed while the special message is
being sent out, which results in degraded transmission
efficiency.
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Further, when the other member (ECU) goes faulty
or disconnected from the network, the state of the
connection is not certain until the check therefor is
carried out again, and hence there is a possibility of
continuing to transfer the transmission right to the
ECU disconnected.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide
a data transmission system for an automotive vehicle
which is capable of enhancing data transmission
efficiency by immediately generating a transmission
right, i.e. initially rendering the transmission right
to a sending end.
It is a second object of the invention to
provide a data transmission system which properly
permits retransmission o:f data when transmission has
not been successfully carried out, while maintaining
the balance between the retransmission of data and the
circulation of the transmission right.
It is a third object of the invention to provide
a data transmission system which is capable of
detecting a disconnection of a unit from a network
without degrading transmission efficiency of the
system.
It is a fourth object of the invention to
provide a method of transmitting data, which permits
prompt confirmations as to whether the transfer of the
transmission right and the transmission of data are
carried out successfully, respectively, thereby
smoothly circulating the transmission right.
To attain the first object of the invention,
according to a first aspect of the invention, there is
provided a data transmission system for a vehicle,
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including a plurality of control systems installed on the
vehicle, and a network bus connecting the pluralit~r of
control systems with each other for circulating a
transmission right through the plurality of control systems
to thereby perform transmission of a message between the
plurality of control systems.
The invention provides in a data transmi;~sion
system for a vehicle, including a plurality of control
systems installed on said vehicle, and a network bus
connecting said plurality of control systems with each other
for circulating a transmission right through said plurality
of control systems to thereby perform transmission of a
message between said plurality of control systems, the
improvement wherein each of said plurality of control
systems comprises: transmitter-receiver means for
transmitting data to or receiving data from the reo~t of said
plurality of control systems via said network bus;
collision-detecting means for detecting a collision of data
transmitted from said transmitter-receiver means with data
transmitted from any of the rest of said plurality of
control systems; mediating means for performing mediation on
said data transmitted from said transmitter-receiver means
and having been detected to be collided with said data
transmitted from any of the rest of said plurality of
control system to direct said transmitter-receiver means to
continue data transmission or stop said data transmission,
for the purpose of avoiding said collision; monitor means
for monitoring said transmission right; and control means
for causing said transmitter-receiver means to start
transmitting data when said monitoring means detects that
said transmission right is not generated or lost from said
system, and causing said transmitter-receiver means to
continue transmitting said data when said collision-
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detecting means does not detect a collision of said data
with data transmitted from the rest of said plurality of
control systems, or when said mediating means directs said
transmitter-receiver to continue data transmission,, wherein
said mediating means compares said data transmitted from
said transmitter-receiver means with said data received via
said network bus from the rest of said plurality o:E control
systems, bit by bit, based on the logic considering one of
logical levels of transmission data as dominant, and the
other of said logical levels~of said transmission data as
recessive, and directing said transmitter-receiver means to
stop said data transmission when said data transmitted from
said transmitter-receiver means and said data received from
said network bus are different from each other.
Preferably, the data transmission system further
comprises transfer means for transferring the transmission
right to a subsequent control system in a predetermined
manner, when the control means controls the transmitter-
receiver means to continue the data transmission until the
data transmission is completed.
Preferably, the transfer means transfers the
transmission right to the subsequent control unit by
increasing an address representative of the each of the
plurality of control systems incorporating the transfer
means by a predetermined number.
To attain the second object of the invention,
according to a second aspect of the invention, there is
provided a data transmission system for a vehicle, including
a plurality of control systems installed on the vehicle, and
a network bus connecting the plurality of control systems
with each other for circulating a transmission right through
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the plurality of control systems to thereby perfornn
transmission of a message between the plurality of control
systems.
The data transmission system according to the
second aspect of the invention is characterized in that each
of the plurality of control systems comprises:
6a
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transmitter-receiver means for transmitting data to or
receiving data from other ones of said plurality of control
systems via said network bus;
transmission failure-detecting means for detecting
failure in transmission of said data;
failure type-identifying means for identifying a type of
said failure in transmission of said data;
retransmission control means for determining a maximum
number of times of retransmission to be permitted according to
said type of failure in transmission identified by said
failure type-identifying means, and for causing said
transmitter-receiver means to retransmit said data so long as
the number of times of retransmission of said data does not
exceed the maximum number of times of retransmission to be
permitted;
wherein the failure type-identifying means comprises
means for detecting whether an acknowledging response is
present, and whether an error in transmission has occurred;
and
wherein said transmission failure-detecting means
comprises monitoring means for determining that said error in
transmission has occurred when data being transmitted does not
coincide with data loaded on said network bus.
Preferably, the type of failure in retransmission is
classified into a case in which no acknowledging response is
detected, and a case in which an error in transmission is
detected.
Preferably, the retransmission control means sets
the maximum number of times of retransmission to be permitted
to a larger value when the error in transmission is detected
than when no acknowledging response is detected.
According to a third aspect of the invention, there
is provided a data transmission system for a vehicle,
including a plurality of control systems installed on the
vehicle, and a network bus connecting the plurality
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of control systems with each other for circulating a
transmission right through the plurality of control
systems to thereby perform transmission of a message
between the plurality of control systems, each of the
plurality of control systems including transmitter-
receiver means for transmitting data to or receiving
data from the rest of them plurality of control systems
via the network bus, transfer destination-setting means
for setting a destination of transfer of the
transmission right, acknowledging response-detecting
means for detecting an acknowledging response output
from another control system having received the
transmission right, and abnormality-detecting means for
detecting abnormality of the system.
The data-transmis:;ion system according to the
third aspect of the invention is characterized in that:
the transfer destination-setting means sets a
subsequent transfer dest:Lnation when no acknowledging
response is detected, and
the abnormality-determining means determines
that the system is abnormal, when setting of the
transfer destination by i:he transfer destination-
setting means has been performed round all of transfer
destinations to be set.
Preferably, the d<~ta transmission system further
comprises time-measuring means for measuring a
predetermined time period elapsed after the start of
the data transmission system, and inhibiting means for
inhibiting the abnormality-determining means from
determining abnormality of the system before the time-
measuring means has measured the predetermined time
period.
Preferably, the transfer destination-setting
means sets the subsequent transfer destination by
increasing an address indicative of the transfer
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destination by a predetermined number.
More preferably, the abnormality-determining
means determines that the setting of the transmission
right has been performed round the all of transfer
destinations to be set, when the address of the
transfer destination becomes identical to an address of
the present control system having the transmission
right.
To attain the fourth object of the invention,
according to a fourth aspect of the invention, there is
provided a data transmission method for connecting a
plurality of control systems installed on a vehicle by
at least one common signal line, and transmitting a
message between the plurality of control systems while
circulating a transmission right through the plurality
of control systems.
The data transmission method according to the
fourth aspect of the invention is characterized in that
the message comprises a first response field for
receiving a first acknowledging response output from a
control system having received the transmission right,
and a second response field for receiving a second
acknowledging response output from a control system
having received data.
Preferably, a processing corresponding to the
first acknowledging response is performed in preference
to a processing corresponding to absence of the second
acknowledging response.
Preferably, the processing corresponding to the
first acknowledging response is waiting for reception
of the transmission right next time or continuation of
transfer of the transmission right, and the processing
corresponding to absence of the second acknowledging
response is retransmission of the data.
To attain the fourth object, according to a
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fifth aspect of the invention, there is provided a data
transmission method for connecting a plurality of
control systems installed on a vehicle by at least one
common signal line, and transmitting a message between
the plurality of control systems while circulating a
transmission right through the plurality of control
systems.
The data transmission method according to the
fifth aspect of the invention is characterized in that:
the message is classified into a first message
having a first response field for receiving a first
acknowledging response output from a control system
having received the transmission right, and a second
message having a second response field for receiving a
second acknowledging response output from a control
system having received data; and
each of the plurality of control systems judges
that transfer of the transmission right is completed
irrespective of whether the second acknowledging
response is detected or not, if the first acknowledging
response is detected when the second message is sent
out therefrom, and does not perform transmission of the
message until the transmission right is acquired next
time, whereas the each of the plurality of control
systems sends out the first message to continue the
transfer of the transmission right when the first
acknowledging response is not detected.
The above and other object, features, and
advantages of the invention will become more apparent
from the following detailed description taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a block diagram showing the whole
arrangement of a control system for an automotive
vehicle according to an embodiment of the invention;
Fig. 2 is a block diagram showing the
arrangement of an electronic control unit appearing in
Fig. 1;
Fig. 3 is a circuit diagram showing details of a
bus interface appearing :in Fig. 2;
Fig. 4a is a diagram showing a format of a
message containing a data unit for transmission between
electronic control units;
Fig. 4b is a diagram showing a format of a
message containing no data unit;
Fig. 5 is a flowchart showing a program for
initially generating altoken (transmission right) when
the token has not been generated or lost;
Fig. 6a to Fig. 6d collectively form a timing
chart which is useful in explaining a manner of
mediation for settling contention for the transmission
right, in which:
Fig. 6a shows bit Nos.;
Fig. 6b shows data transmitted from a node l;
Fig. 6c shows data transmitted from a node 2;
and
Fig. 6d shows logical levels on a bus;
Fig. 7 is a flowchart showing a program for
terminating the data transmission; and
Fig. 8 is a flowchart showing a program for
transferring the transmission right.
DETAILED DESCRIPTION
The invention will described in detail with
reference to drawings showing an embodiment thereof.
Fig. 1 shows the whole arrangement of a control
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system for an automotive vehicle according to the
embodiment comprising electronic control units
(hereinafter referred to as "the ECU's") 1 to 5
connected with each other via a network bus 6. An ENG
control ECU 1 controls operation of an engine in
response to operation of an accelerator pedal operated
by a driver of the vehicle, etc. An MISS control ECU 2
controls an automatic transmission of the vehicle
according to the operating conditions of the engine. A
TCS control ECU 3 detects a slip of driving wheels and
controls an output torque of the engine. A suspension
control ECU 4 controls a suspension (active suspension)
system of the vehicle depending on the operating
conditions of the engine. A brake control ECU 5
detects a slip of wheels and controls braking
operation. These ECU's 1 to 5 are required to be
permitted to mutually monitor control parameters and
operating parameters detected by sensors, some of the
sensors being collectively shown in Fig. 2, and hence
are connected to each other by way of the network bus 6
for transmission of data necessitated by each other.
Fig. 2 shows the arrangement of the ENG control
ECU 1 which comprises a central processing unit
(hereinafter referred to as "the CPU") 101, an
input/output interface 104 connecting a plurality of
sensors 11, and a plurality of actuators, such as fuel
injection valves, to the CPU 101. The CPU 101 is
connected via a bus line 107 to a RAM (Random Access
Memory) 102, a ROM (Read Only Memory) 103, and a
communication control IC (Integrated Circuit) 105. The
communication control IC 105 is connected via a bus
interface 106 to the network bus 6.
The CPU 101 determines control parameters based
on output signals from the sensors 11 according to a
program stored in the ROM 103 for driving the actuators
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12. The RAM 102 temporarily stores data of results of
computation. The communication control IC controls
transmission of a message to the network bus and
reception of a message from the network bus.
Fig. 3 shows details of the bus interface 106
connected to the communication control IC 105, and the
network bus 6 comprised of twisted pair lines 6b and 6c
connected at both ends o1. thereof to each other via
respective terminal resistances 6a, 6a.
The communication control IC 105 has a first
sending terminal connected to a base of a transistor
119 via a resistance 115.. The transistor 119 has an
emitter thereof connected to a power supply line VSUP
and a collector thereof connected via a resistance 116
to an inverting input terminal of a comparator 111 and
to one 6b of the twisted pair lines 6b and 6c.
The communication control IC 105 has a second
sending terminal connected to a base of a transistor
120 via a resistance 117. The transistor 120 has an
emitter thereof grounded and a collector thereof
connected via a resistance 118 to a non-inverting input
terminal of the comparator 111 and to one 6c of the
twisted pair lines 6b and 6c.
The non-inverting input terminal of the
comparator 111 is connected via a resistance 112 to the
power supply line VSUP, and also via a resistance 113
to the inverting input terminal of the comparator 111.
The comparator 111 has it:s inverting input terminal
grounded via a resistance 114, and delivers an output
signal therefrom to a receiving terminal of the
communication control IC 105.
In the circuitry ~>hown in Fig. 3, the
resistances 116 and 118 are each set to approximately
30 SZ, the resistances 112 and 114 to approximately 2 k
~, the resistance 113 to approximately 200 S~, and the
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terminal resistances 6a to approximately 100
The first and second sending terminals of the
communication control IC i05 are supplied with pulse
signals reverse to each other in~phase. when the first
sendir.~.g terminal is at a low level and the second
sending terminal is at a high level, both the
transistors 119 and 120 are turned on to set the
voltage of the one twisted pair line 6b at the high
level and the other twisted pair line 6c at the low
level. When the first sending terminal is at the high
level and the second sending terminal is at the low w
level, both the transistors 119 and 120 are turned off
to set the voltage of the one twisted pair line 6b at
the low level and the other twisted pair line 6c at the
high level. Thus, a signal is sent out to the network
bus 6.
As the potential of the one twisted pair line 6b
goes high and low, the output from the comparator 111
goes low and high, thereby receiving a signal loaded on
the network bus 6.
The ECU's 2 to 5 are basically constructed in
the same manner. Therefore, even if one of the ECU's
sends ~~ut a signal which sets the voltage of the one
twisted pair line 6b at the low level (i.e. sets the
voltage of the other twisted pair line 6c at the high
level), when another ECU sends out a signal which sets
the vo:Ltage of the one twisted pair line 6b at the high
level, the state of the voltage of the twisted pair
line 6b is set to the high level. Therefore, in the
preseni~ embodiment, a state in which the one twisted
pair line line 6b is at the high level (the other
twiste<3 pair line 6c is at the low level) is defined as
a dominant state, and an opposite state thereof as a
recess _ve state.
Next, a method of data transmission between the
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ECU's; will be described. In the present embodiment, a
token passing method is employed. This takes into
consideration the fact that compared with a CSMA/CD
(Carrier Sense Multiple Access with Collision
5 Detection) method which is capable settling the
collision, the token passing method is advantageous in
respect of an electric delay on the network bus, and is
capable of easily determining the maximum message delay
time period, allowing the network system to be be
70 designed easily.
Fig. 4a and Fig. 4b show formats of messages
used in data transmission in the present embodiment.
Fig. 4a shows a format of a data message (second
message) for sending a token (representative of the
15 transmission right) and data, while Fig. 4b shows that
of a token message (first message) for sending the
token alone. In the following description, the ECU's
const_tuting the network system will be referred to ws
the nodes 1 to 5.
In Fig. 4a, a field F1 (SOM) notifies the start
of a message, which is formed by one dominant bit.
This field is used for synchronization of all the nodes
constituting the network system.
A field F2 (TA) designates an address of a
destination node to which the token is to be
transferred, which is formed by four bits of data. The
node address is set e.g. to one of values 0 to 4 in a
manner corresponding to the ECU's 1 to 5.
A field F3 (CTL) designates a kind of message
(token message or data message).
A field F4 (DATA UNIT) is a data unit comprised
of a D:V (Destination Node) field designating a node or
nodes which should receive data contained in a DATA
field, a DLC (Data Length)field designating the length
of a byte of the DATA field, an ID (Identifier) field
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t6
forming an identifier of the data, and the DATA field
containing information to be transmitted.
In this connection, the length of the DATA field
is variable as can be presumed from the above
description, and the total length bf the data unit is
variable within the range of 32 to 96 bytes.
A field FS (FCS) is a CRC (Cyclic Redundancy
Check) field comprised of a sequence (CRC character
seauence) of characters for error detection having 16
bits ~~btained by using the following equation-(1) as a
generating polynomial:
Generating polynomial = X16 + X12 + XS + 1
A delimitter (dividing character) having one
recessive bit is interposed between the field F5 and
the f_':eld F6.
A field F6 (DACK) is a second response field
into which a data-acknowledging response (second
acknourledge character) should be written by a node
havinct normally or safely received the data, which is
formed by an acknowledge slot having two bits. A
sending node sends a message having the acknowledge
slot as recessive bits, and the node or nodes which
is/are designated in the message as one or ones to
receive the information and has/have normally or safely
received the data makes) the data-acknowledging
response by overwriting two dominant bits therein. A
delimitter having two recessive bits is interposed
between the fields F6 and F7.
A field F7 (TACK) is a first response field into
which a token-acknowledging response (first acknowledge
character) should be written by a node having normally
or safely received the token, which is formed by an
acknowledge slot having two bits, similarly to the
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field F6. The sending node sends a message having the
acknowledge slot as recessive bits, and the node having
received the token makes the token-acknowledging
response by overwriting two dominant bits therein. A
delimitter formed by two recessive bits is interposed
between the field F7 and the field F8.
A field F8 (EOM) designates the end of the
message, and is formed by six recessive bits.
In the present embodiment, the field F7 and the
field F6 are provided as fields into which
acknowledgement of the token and acknowledgement of
data are made, respectively, which makes it possible
for a sending end to promptly confirm whether or not
the transfer of the token and the transmission of data
have aeen successfully carried out.
The token message shown in Fig. 4b is
constructed such that the fields F4 to F6 are deleted
from the data message, and a delimitter is interposed
between the fields F3 and F7.
Next, a method of circulating the token
(tran;sferring the token round the ECU's) will be
described.
If a node having received the token has data or
information to be transmitted, it has to transfer the
token together with the data. If the node has no data
or information to be transmitted, it has to transmit
the token alone. A node to which the token is to be
transferred is a node designated in the field F2 (TA).
The t«ken address is normally set by adding a value of
one t« the address of the sending node itself, and a
messa~~e continues to be sent out until a token-
acknocNledging response is detected, by sequentially
increasing the token address by an incremental value of
1. However, when a calculated value of the token
addreas reaches a value of i6, the token address is set
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to 0, thus circulating token address through values of 0 to
15.
When the node corresponding to the token address set
in the message has received the token, it overwrites two
dominant bits into the acknowledge slot of the field F7
(TACK), thereby making the token-acknowledging response. When
the token-acknowledging response is thus overwritten and the
messager normally terminates in the field F8 (EOM), the sending
node having sent the token completes the transfer of the
token, and the receiving node has acquired the token.
Next, a manner of detecting failure in transmission
of a message will be described.
When roughly classified, there are two types of
failures in transmission: one in which there has been no
transmission error but no data-acknowledging response is
overwritten in the field F6 (DACK) of the acknowledge slot,
and they other in which a transmission error has been detected
during the transmission of a message. When no data-
acknowledging response has been made, this type of failure of
transmission is detected by the sending node itself.
On the other hand, the transmission error is
detected by monitoring of data, detection by CRC, detection of
bit stuff error, and a message format check.
According to the error detection by monitoring of
data, a transmission error is detected when data which a
sending node is transmitting does not coincide with data
loaded on the bus. However, this monitoring of data is
inhibited with the acknowledge slots of the fields F6 and F7,
and one recessive bit subsequent thereto.
According to the error detection by CRC, a
transmission error is detected when an error is found
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as to CRC characters set in the field F5 (FCS), and
this detection is performed by nodes other than the
sending node.
According to the bit stuff error detection, it
i_> determined that there is an error in transmission
when more than 5 consecutive bits designate the same
logical state, and this detection is performed by nodes
other than the sending node. However, the fields F6
(I>ACK), F7 (TACK), F8 (EOM) and the delimitters are
e~:ecuted from objects of monitoring.
According to the error detection by the message
format check, an error is detected when an illegal
logical state is found in the fields of the fixed-
logical-state bits (the fields F3, F8 and the
delimitters), and this type of error detection is
performed by nodes other than the sending node.
When any of the above-described errors occurring
during transmission is detected, a node having detected
tree error immediately sends out an error message (six
consecutive dominant bits), whereby even if a
transmission error is detected by a node or nodes other
than the sending node, the sending node can recognize
the transmission error.
Next, a procedure of generating the token or
initially rendering the token to one of the nodes when
tree token has not been generated or lost from the data
ti-ansmission system will be described with reference to
Fig. 5 and Fig. 6.
The communication control IC 105 of each of the
EC:U's 1 to 5 determines at a step S1 of Fig. 5 whether
oz: not the network bus i.s idling, to determinate
whether the data transmission system is in a state in
which the token has not been generated immediately
ai_ter the start of system, or has been lost due to
failure of a node having received the token. If the
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2U
answer to this question is negative (NO), i.e. if
another ECU is sending a message, the present program
is immediately terminated.
On the other hand, if the network bus 6 is idle,
i.e. no other ECU's are sending any message, the
present ECU starts data transmission via the
communication control IC 105 and the bus interface 106
at a step S2, assuming that the present node has
acquired the token. Then, data sent from the present
node is compared with data on the network bus 6 bit by
bit to determine whether both the data are identical to
each other at a step S3. If the answer to this
question is affirmative (YES), i.e. the data sent out
and the data on the network bus coincide with each
~5 other, it means that there is no contention between the
data sent out from the present node and data from other
nodes, or the present node remains undefeated in
contention for acquiring the token, and hence data
transmission is continued assuming that the present
node has not lost the token yet. That is, the present
program proceeds to a step S4, where it is determined
whether or not transmission of the whole sequence of
data has been completed. If the answer to this
question is negative (NO), the program returns to the
step S3, where data subsequently sent out is compared
with data loaded on the network bus, in the same manner
as described above.
It goes without saying that there is a case in
which the present node is found to be defeated in
contention for acquiring the token to stop data
transmission when the above-described procedure is
carried out. Further, as a method of determining
whether the data sent from the present node and the
data loaded on the system bus coincide with each other,
the above-mentioned method of the error detection by
- CA 02226421 1998-03-09
21
monitoring data is utilized for determining that the
data sent out and the data loaded on the system bus do
not coincide with each other. In the present case,
more specifically, the coincidence of the data is
determined by calculating an exclusive OR of the data
sent out and the data received from the network bus 6.
On the other hand, if the data sent out from the
present node is different from the data loaded on the
network bus 6, it means that there has been a
contention for the token with other nodes, and the
present node has been defeated in the contention, so
that the data transmission is stopped at a step S5,
followed by terminating the present program.
If it is determined at the step S4 that the
whole sequence of data has been sent out, i.e. if it is
determined that the present node remains undefeated
throughout the contention for acquiring the token, it
is~ determined at a step S6 whether or not the transfer
of the token has been completed, by making a check for
the token-acknowledging response. If the transfer of
the token has not been completed, a value of 1 is added
to the token address of the token message, and then the
resulting token message is sent out to the network bus
6 at a step S7. The steps S6 and S7 are repeatedly
carried out until the transfer of the token is
completed, whereupon the present program is terminated.
Further, in determining a winner of contention,
data formed by an identical sequence of bits is
actually sent out a plurality of times for prevention
of an erroneous determination due to noise or the like.
Next, details of a manner of determining a
winner of the contention will be described with
reference to Fig. 6a to Fig. 6d.
Let it be assumed that data are transmitted from
Node 1 and Node 2 as shown in Fig. 6b and Fig. 6c,
- CA 02226421 1998-03-09
22
respectively. As described hereinbefore, a bit in the
logical state "1" is a dominant bit, and a bit in the
logical state "0" is a recessive bit. If contention
occurs between the dominant bit and the recessive bit,
the logical state on the network bus becomes equal to
..1...
In the case of data shown in Fig. 6b and Fig.
6c, bits corresponding to the bit numbers 1 to 4 shown
in Fig. 6a are in the same logical states,
respectively, and the logical states of the data sent
from Node 1 and Node 2, and the logical state of the
network bus are all equal to each other. Accordingly,
Node 1 and Node 2 both continue to send out respective
messages from bit No. 1 to bit No. 4.
However, at bit No. 5, the logical state of data
sent from Node 1 is equal to "1", whereas the logical
state of data sent from Node 2 is equal to "0".
Accordingly, the logical state of the network bus
becomes equal to the logical state "1" of the dominant
bit sent from Node 1. Therefore, Node 1 having sent
the dominant bit determines that it has not lost the
token and continues to send the message, whereas Node 2
having the sent the recessive bit determines that it
has lost the token and ceases to send the message.
In this connection, Fig. 6a to Fig. 6d show a
case where two nodes are in contention for the token.
However, actually, there can occur a case in which a
contention for the token arises among more than two
nodes. However, it is impossible for all the nodes to
continue sending the same sequence of data, and
eventually, one node is necessarily determined to
remain undefeated in the contention, without any
inconveniences.
As can be clearly understood from the above
description, according to the present invention, when
- CA 02226421 1998-03-09
23
the control system is started or a node having received
the token is in failure, a token is generated or
initially given to one of the nodes by contention for
the token as described above, and then the token is
circulated through or transferred round the nodes.
This makes it possible to promptly generate the token
by giving a chance of acquiring the token equally to
all the nodes, enabling the system to function
efficiently.
Further, the present invention is not limited to
the above embodiment, but as a manner of mediation of
contention, the logical state "0" may be used for a
dominant bit and the logical state "1" for a recessive
bit, inversely to the above embodiment. Further, after
the token has been generated through contention, a node
to which the token is first transferred is not
necessarily restricted to a node having a node address
following the address having initially acquired the
token, but the token may be first transferred to a
predetermined node having the smallest node address,
then permitting the node to circulate through the nodes
in a predetermined cycle.
Next, a procedure of processing performed when
no data-acknowledging response has been received after
a sending node has sent a data message. In the
following description, the first acknowledge character
to be overwritten into the field F7 is referred to as
"the token ACK", while the second acknowledge character
to be overwritten in the field F6 as "the data ACK".
(1) When the token ACK is not detected and the
data ACK is detected:
The token data address is increased by an
incremental value of 1 and then the resulting token
message is sent out. This is for transferring the
token alone to a node subsequent to the node to which
- CA 02226421 1998-03-09
24
the token has not been successfully transferred, since
reception of the data written in the field F4 has been
acknowledged.
(2) When the token ACK is detected, and the
data ACK is not detected:
Since the transfer of the token is completed,
retransmission of data is not carried out. The data is
retransmitted, if possible, when the token is acquired
next time.
(3) when neither r_he token ACK nor the data ACK
is detected:
The token address is increased by an incremental
value of 1 and the token message containing the
resulting token address is transmitted, but the
retransmission of data is not carried out. Thus, the
circulation of the token is performed in preference to
the transmission of data to permit smooth circulation
of the token. Further, the data is transmitted again,
if possible, when the token is acquired next time.
As described above, even if the data ACK is not
detected, it is judged, so long as the token ACK is
detected, that the transfer of the token is completed,
and the retransmission of data is inhibited. Further,
when neither the data ACK nor the token ACK is
detected, only the transfer of the token is tried again
without retransmitting the data, whereby it is possible
to circulate the token smoothly. The preference is
given to the transfer of the token since the
retransmission of data performed immediately after
detection of a transmission error requires the maximum
delay time of the system to be set to a longer time
period than when the transfer of the token is
preferentially performed as in the present embodiment.
Although in the above example, when neither the
token ACK nor the data ACK is detected, the token
CA 02226421 1998-03-09
message is permitted to be sent out immediately, and at
the same time retransmission of data is inhibited, this
is not limitative, but the transfer of the token may be
performed after retransmission of data is tried one or
5 two times. Fig. 7 shows this variation of the
procedure of transmission control performed by the
communication control IC 105 for terminating the
transmission upon completion of the sending of the
message or upon detection of an error message.
10 In the following description, it should be
understood that an error in transmission is detected by
a sending node or a receiving node, whereupon an error
message is sent out from the node having detected the
error, thereby terminating the transmission.
15 At a step S21 of Fig. 7, it is determined
whether or not an error has occurred to transmission.
If the answer to this question is negative (NO), it is
determined at a step S22 whether or not the transfer of
the token is completed (whether or not the token ACK is
20 detected). If the transfer of the token has been
completed, first and second counters CTl, CT2, referred
to hereinafter, are reset at a step 530, followed by
terminating the present program. If the answer to the
question of the step S22 is negative (NO), i.e. if no
25 error has occurred during the transmission, but the
transfer of the token is not completed, the program
proceeds to a step S23, where it is determined whether
or not the data has been successfully transmitted
(whether or not the data ACK is detected). If it is
determined that the data has been successfully
transmitted, the transfer of the token is performed at
a step 529, and then the first and second counters CT1,
CT2 are reset at the step 530, followed by terminating
the program.
On the other hand, if the answer to the question
CA 02226421 1998-03-09
26
of the step S23 is negative (NO), i.e. if no error has
occurred during the transmission, but neither the
transfer of the token nor the transmission of the data
is successfully carried out (neither the token ACK nor
the data ACK is detected), the program proceeds to a
step S24, where an count value of the first counter CT1
is increased by an incremental value of 1, and it is
determined at a step S25 whether or not the resulting
count value of the first counter CT1 is equal to a
0 first predetermined value C1 (which is set e.g. to a
value of 2). When this step is first carried out, CT1
< C1 holds, so that retransmission of the message which
has not been successfully transmitted is performed at a
step S28, followed by terminating the program. If the
acknowledging responses (the token ACK and the data
ACK) continue not to be detected thereafter until CT1 =
C1 holds at the step S25, the program proceeds
therefrom to the step 529, where the token is
transferred by the token message, and the counters CT1,
CT2 are reset, at the step 530, followed by terminating
the program.
If the answer to the question of the step S21 is
affirmative (YES), i.e. if an error has occurred to
transmission, a count value of the second counter CT2
is increased by an incremental value of 1 at a step
S26, and it is determined at a step S27 whether or not
the resulting count value of the second counter CT2 is
equal to a second predetermined value C2 (which is set
e.g. to a value of 5). When this step is first carried
out, CT2 < C2 holds, so that the retransmission of the
message which has not been successfully transmitted is
performed at the step S28, followed by terminating the
program. If the transmission error continues to occur
until CT2 = C2 holds at the step 527, the program
proceeds therefrom to the steps S29 arid S30, followed
- CA 02226421 1998-03-09
27
by terminating the program.
According to the processing of Fig. 7, when
transmission of a data message has not been
successfully carried out:, retransmission of the message
is carried out up to the' maximum number C1 - 1 of times
when the data- and token-acknowledging responses
(acknowledge characters DACK, TACK) are detected, or
alternatively up to the maximum number C2 - 1 of times
when an error in transmission has occurred. If
transmission of the message cannot be successfully
carried out even if it is tried the maximum number of
times set as above, the token is transferred by the
token message.
Since the second predetermined value C2 is
larger than the first pi-edetermined value C1, the
maximum number of times of retransmission is larger for
an error in transmission than for no acknowledge
characters DACK and TACK. This is because in the case
where no acknowledge characters are detected, there is
a high possibility of absence of a node or nodes to
receive the message, which means a high possibility of
failure in transmission even if the message is
retransmitted, whereas in the case where an error in
transmission is detected, there is a high possibility
of the error having been caused by an external
disturbance, which mean; a high possibility of success
in retransmission.
Further, if the transmission continues to be
unsuccessful, the token is transferred by the token
message to thereby circulate the token smoothly.
As described above, according to the present
embodiment, when transmission of a message is
unsuccessful, the message is retransmitted a number of
times dependent on a po=>sible cause of failure in
transmission, and if the transmission still continues
- CA 02226421 1998-03-09
28
to be unsuccessful, the token is transferred by the
token message, thereby reducing the number of useless
retransmissions to circu:iate the token smoothly. As a
result, the efficiency o:E the data transmission by the
data transmission system as a whole can be enhanced.
Next, a manner of detecting abnormality of the
system according to the :invention will be described
with reference to Fig. 8.
Fig. 8 shows a procedure of one node
transferring the token to the subsequent node. First
at a step S31, the present node sets a token address TA
to a value obtained by adding a value of 1 to an
address SNA of its own, and transmits a data message or
a token message containing the resulting token address
at a step 532. Then, it is determined at a step S33
whether or not a token-acknowledging response (the
token ACK) acknowledging receipt of the token has been
detected. If the token ACK has been received or
detected, it is determined at a step S34 that the
system is normally functioning, followed by terminating
the program.
If the token ACK leas not been detected, the
token address TA is increased by an incremental value
of 1 at a step 535, and then it is determined at a step
S36 whether or not the rc=sulting token address TA is
identical to the address SNA of the present node. when
this step is first carried out, TA is not equal to SNA,
and hence the program proceeds to a step 537, where the
updated token message is sent out, followed by the
program returning to the step 533. If the token ACK
continues not to be detected thereafter, the token
address TA is sequential:Ly increased. In the present
embodiment, when the tok<=_n address TA becomes equal to
15, the subsequent token address TA is set to 0, and
then progressively incre<~sed in the same manner. For
- CA 02226421 1998-03-09
29
example, if the present node has an address SNA of 2,
the token address TA is sequentially changed in the
order o f 3 -i 4 -i . . . . -~ 1 S -' 0 -' 1 -~ 2 , and when
the token address TA becomes equal to the address SNA
of the present node, the program proceeds to a step
538, where it is determined whether or not a
predetermined time period has elapsed (e. g. a time
period required to permit. all the ECU's to become
operative or active after the start of the control
system, e.g. one second) has elapsed. If the
predetermined time period has not elapsed, transmission
of the token message is resumed at the step S35 with
the token address TA being started from TA = SNA + 1,
whereas if the predeterm:Lned time period has elapsed,
it is determined at a step S39 that the system is
abnormal, followed by terminating the program. The
abnormality of the systern is ordinarily interpreted as
a state of the present node being disconnected from the
network bus, although it is theoretically possible to
assume a case in which all the other nodes are
disconnected from the network bus or in failure.
Further, the reason for _Lnhibiting the abnormality
determination until the predetermined time period
elapses after the start of the control system is that
each node has its own rise time, i.e. the nodes, i.e.
the ECU's, require different time periods before they
become operative, respect=ively, and before the
predetermined time period elapses, there can be a case
in which some ECU cannot respond to the token message.
According to the I~ig. 8 processing, the
abnormality of the system can be determined while
performing the transfer of the token, so that other
processings can be continued, without being
interrupted, which is impossible for the method
employing a special message. This makes it possible to
CA 02226421 1998-03-09
3U
detect the abnormality of the system without degrading
the transmission efficiency of the system.
In addition, the prompt detection of abnormality
of the system described above is possible since the
data transmission system for an automotive vehicle
incorporates a relatively small number of nodes (in the
present embodiment, the maximum number thereof is 16)
connected to the network bus. That is, the method of
detecting abnormality employed by the present system is
markedly effective for a system in which the token
passing method is used with a relatively small number
of nodes.
