United States Patent [!9J
`Wolfsgruber et al.
`
`[54] SYSTEM FOR COMMUNICATION
`BETWEEJ'Ii A MASTER AND SLAVE
`PROCESSING
`
`[75]
`
`Inventors: Arturo Wolfsgruber, Milan; Sandro
`Storti, Sesto San Giovanni; Alberto
`Coen, Milan, all of Italy
`[73] Assignee: SGS-Tbomson Microelectronics S.r.l.,
`Italy
`[21] Appl. No.: 519,288
`[22] Filed:
`May 4, 1990
`[30]
`Foreign Application Priority Data
`May 4, 1989 [IT]
`Italy ............................... 67327 A/89
`Int. Cl.s ................................................ H04J 3/02
`[51]
`[52] u.s. Cl ....................................... 370/85.1; 370/67
`[58] Field of Search ................. 370/100.1, 85.13. 85.6,
`370/94.3, 85.1; 340/825.44; 455/343
`References Cited
`U.S. PATENT DOCUMENTS
`4,715,031 12/1987 Crawford et al. ................. 370/85.6
`4, 719,622 1/1988 Whipple et al. ................... 370/85.1
`4,780,620 10/1988 Hogberg et al. ................. 370/100.1
`4,847.756 7/1989 Ito et al. ............................. 370/85.1
`
`[56]
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005121386A
`[II] Patent Number:
`[45] Date of Patent:
`
`5,121,386
`Jun. 9, 1992
`
`4,942.571 7/1990 Moller et al. .................... 370/85.13
`4,958,343 9/1990 Abramovici et al. .............. 370/85.1
`
`Primary Examiner-Stephen Chin
`Assistant Examiner-Dang Ton
`Attorney, Agent, or Firm-Gifford, Groh, Sprinkle,
`Patmore and Anderson
`ABSTRACT
`[57]
`A communication system of the multiplex type between
`a master processing unit incorporating a microproces(cid:173)
`sor and slave units associated in particular with electri(cid:173)
`cal devices in a vehicle for activating or controlling at
`least one electrically functioning component of the
`corresponding device the slave units being connected in
`groups to the master unit by means of corresponding
`communication channels, and in which these slave units
`include logic means for the exchange of communication
`messages with the master unit and are capable of inde(cid:173)
`pendently initiating transmission towards the master
`unit; such messages in particular include a first field for
`identification of the slave unit which is sending or is to
`receive the communication, a second data field, and a
`preliminary field used to activate such units from a
`resting state of minimum power consumption.
`
`25 Claims, 4 Drawing Sheets
`
`30~
`
`31
`.\--27
`
`WEBASTO EX. 1029
`WEBASTO ROOF SYSTEMS, INC. v. UUSI, LLC
`IPR2014-00650
`Page 1
`
`

`

`U.S. Patent
`
`June 9, 1992
`
`Sheet 1 of 4
`
`5,121,386
`
`5
`
`Fig.1
`
`8
`
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`
`Page 2
`
`

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`Page 3
`
`

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`51
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`. FIRST
`
`Page 4
`
`

`

`U.S. Patent
`
`June 9, 1992
`
`Sheet 4 of 4
`
`5,121,386
`
`-CJ)
`
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`Page 5
`
`

`

`1
`
`5,121,386
`
`SYSTEM FOR COMMUNICATIO]'; BETWEE]'; A
`MASTER AND SLAVE PROCESSING
`
`2
`by means of one communication channel which is ac(cid:173)
`cessible to a plurality of the said units. characterized in
`that the said slave units include logical means for per(cid:173)
`forming the exchange of communication messages with
`5 the said master unit, and are capable of independently
`initiating transmissions to the said master unit.
`
`BACKGROUND OF THE INVENTION
`This invention relates to a communication system of
`the multiplex type, that is with an information channel
`which is accessible to a plurality of users, provided
`between a master processing unit and slave units with
`the possibility that information exchange can be initi- 10
`a ted from one of the slave units. In particular the com(cid:173)
`munication system according to this invention can be
`applied to a plurality of units associated with the electri(cid:173)
`cal devices in a vehicle, and especially for activation
`and control of the electrical devices fitted to a vehicle 15
`door, for example, the window winding device, the
`door locking device, the device actuating various elec(cid:173)
`trical components in an outside rear-view mirror and
`the manual control switch device for operating the
`components of the various abovementioned devices as 20
`described in Italian patent application No. 67158-A/89
`lodged on the Mar. 7, 1989 entitled: "Activation and
`control system for a plurality of electrical devices in a
`vehicle".
`As known, multimaster systems in which each unit 25
`has the characteristics of a master unit and is therefore
`capable of communicating directly with every other
`unit are used in communication systems between vari(cid:173)
`ous units. This has disadvantages in that:
`all the units must be approximately equal in complex- 30
`ity
`because all the units are connected by means of a
`single data transmission line. A fault in the latter
`may cause failure of the entire system if redun(cid:173)
`dancy is not provided, but this entails costly dupli- 35
`cation and operational difficulties.
`The structure of the messages is complex, either be(cid:173)
`cause they have to include double addressing, or be(cid:173)
`cause of the need to interpret all messages by a single
`unit.
`therefore been con(cid:173)
`Master-slave systems have
`structed in which there is a central master unit which
`controls all communication sending commands to, in(cid:173)
`terrogating or synchronizing the slave units, which in
`turn can only transmit after these communications have 45
`been received. A result of this however is that the mas-
`ter unit must always be active whenever communica(cid:173)
`tion is required with any slave unit. In order to over(cid:173)
`come this disadvantage while maintaining the structure
`of the master-slave system additional transmission lines 50
`dedicated to communication requests are required.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`In order to provide a better understanding of this
`invention a particular embodiment will now be de(cid:173)
`scribed purely by a way of a non-restrictive example
`with reference to the appended drawings in which;
`FIG. 1 is a diagrammatical view from above of a
`motor vehicle to which the communication system for
`activation and control of a plurality of electrical devices
`constructed according to this invention is fitted,
`FIG. 2 is a simplified block diagram of the connec(cid:173)
`tions between the various units in the system in FIG. 1,
`FIG. 3 is an illustration of a communication message
`between units in the system in FIG. 1, and
`FIG. 4 is an illustration of a communication time
`sequence between units in the system in FIG. 1.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`The communication system according to this inven(cid:173)
`tion between various slave units and a master unit, and
`therefore between various slave units via a master unit,
`applies to local transmission networks of the multiplex
`type, and conveniently to multiplex networks in motor
`vehicles, for example of the type described in the above-
`mentioned Italian patent application No. 67158-A/89
`lodged on the Mar. 7, 1989, the contents of which are
`incorporated in this description by mere reference
`where necessary.
`FIG. 1 therefore illustrates a motor vehicle 1 includ(cid:173)
`ing actuator devices provided respectively with slave
`units connected with a master by means of multiplex
`40 connections, forming a communication system accord(cid:173)
`ing to this invention. This motor vehicle 1 has two front
`doors 2 and 2', and two rear doors 3 and 3', illustrated
`in the open position. A main control master unit 5 com-
`prising a microprocessor 6 is housed close to dashboard
`4 and from this lead cables 7, 7', 8 and 8' and 9 respec(cid:173)
`tively, each of which consists of a first electrical power
`supply conductor 10, a second data signal transmission
`conductor 11 and a third conductor 12 connected to
`earth.
`Cables 7 and 7' go to front doors 2 and 2' respec-
`tively, while cables 8 and 8' go to rear doors 3 and 3'.
`Each of these cables is progressively connected by
`means of corresponding branches from the three con(cid:173)
`ductors to a corresponding slave unit 27 which is con-
`55 nected respectively to a manual control switch device
`14, an electrical control device 15 for an outside rear(cid:173)
`view mirror 16, a door locking device 17 and a window
`winding device 18 for the activation and control
`thereof. In particular this slave unit 27 conveniently
`60 includes a printed circuit to which are connected a first
`integrated circuit for the distribution of electrical
`power by means of an activating component (e.g. a
`small direct current electric motor) of the correspond(cid:173)
`ing device with which slave unit 27 is associated, and a
`65 second integrated circuit for the processing of data
`signals relating to the operation of that component.
`These first and second integrated circuits form a logic
`unit and may conveniently include specific logic cir-
`
`SUMMARY OF THE INVENTION
`The object of this invention is to provide a communi(cid:173)
`cation system of the multiplex type between a master
`processing unit and slave units in which each slave unit,
`although having the simplified structure of a slave unit,
`can initiate transmission to the master unit so as to over(cid:173)
`come the disadvantages mentioned above, with particu(cid:173)
`lar advantage in application to the communication sys(cid:173)
`tem between a plurality of electrical devices .in a vehi(cid:173)
`cle, where it is important to have a relatively simplified
`system, but with a high guarantee of satisfactory perfor(cid:173)
`mance, in order to reduce production and installation
`costs.
`In accordance with this invention a communication
`system is provided between at least one master unit and
`slave units which are connected to the said master unit
`
`Page 6
`
`

`

`5,121,386
`
`3
`cuits for a microprocessor, solid state switches. etc., and
`may form circuits for protection against voltage and
`current overloads, control and diagnostic circuits, etc.
`In the case of device 14 with manual control switches
`the first integrated circuit is missing, in that there is no 5
`power activation, whereas in the case of device 15 for
`electrical control of the outside rear-view mirror 16
`there will be more than one activating member, in that
`the various electrical components activating orientation
`movements of the reflecting surface of the rear-view 10
`mirror, for altering the orientation of the rear-view
`mirror body with respect to the door, may be con(cid:173)
`trolled, and a supply may be provided to the compo(cid:173)
`nents heating the reflecting surface.
`In the case of cables 8 and 8' for doors 3 and 3' the 15
`connection with electrical control device 15 for outside
`rear-view mirror 16 will obviously be missing. Cable 8
`also passes by means of a branch 26 to a slave unit 27
`associated with a device 28, similar to device 17, for
`locking and releasing a boot 30, while cable 8' passes via 20
`a branch 26' to a slave unit 27 associated with a device
`28', also similar to device 17, for locking and releasing a
`flap 31 providing access to a fuel filler cap for motor
`vehicle 1.
`Cable 9 in turn is progressively connected by means 25
`of corresponding branches to three conductors, two
`relating to slave units 27 associated respectively with a
`first and a second rrianual control switch device 32 and
`33 placed in a zone 34 (console) between the front seats
`capable of controlling devices 15 for electrical control 30
`of outside rear-view mirrors 16 and window winding
`devices 18.
`As is illustrated in greater detail in FIG. 2, the main
`control master unit 5 which is connected to a supply
`battery 40 is in turn connected to slave units 27 con- 35
`nected for example to cable branch 7 by means of con(cid:173)
`ductor 10 providing a positive electrical power supply,
`a conductor 11 for the transmission of data signals and
`a conductor 12 providing a connection to earth. Con(cid:173)
`nection of the various slave units 27 to transmission 40
`conductor 11 is of the "wired and" type, in which a
`return resistor 41 is connected between conductor 11
`and positive power conductor 10 in master unit 5, so
`that the dominant logic level is a "low" logic level, and
`is subordinate to any of the units which initiates trans- 45
`mission. In both master unit 5 and slave units 27 trans(cid:173)
`mission conductor 11 is in fact connected to the input to
`corresponding data receipt block 43, while a switch
`block 44 with a switch which is controlled by a data
`message transmission block 45 is connected between 50
`transmission conductor 11 and earth conductor 12.
`These blocks 43 and 45 form the logic elements of the
`unit, and the coding for unit information is therefore of
`the type in which the duration of pulses of constant
`amplitude equal to the supply voltage is modulated. 55
`Logic value "1" is coded by a high/low ratio of more
`than unity, and vice versa for logic level "0". The con(cid:173)
`nection structure described with the return resistor, the
`switch block and the data receipt and transmission
`blocks are repeated in master unit 5 for the other com- 60
`munication conductors 11, 11', 11" ... , for the other
`cables, and other corresponding members are indicated
`by the same numbers and indices.
`The message sent by any one of units 5 or 27 on trans(cid:173)
`mission conductor 11 has a characteristic time course 65
`shown in FIG. 3, in which starting from a "high" rest(cid:173)
`ing level of conductor 11, at which the transmission line
`is not occupied, there is a first message start field 50 in
`
`4
`which transmission conductor 11 is altered to the "low"
`level by closing switch block 44 which is controlled by
`transmission block 45 of the corresponding unit initiat(cid:173)
`ing the exchange, then there is a second address field 51
`conveniently consisting of six identification bits for the
`slave unit 27 which is transmitting, the logic level "1"
`or "0" of which is given by modulation of the closing
`time for switch block 44 controlled by block 45, then
`there is a third data field 52 conveniently consisting of
`four bits coding the command or message which has
`been transmitted, and a further check field 53 conve(cid:173)
`niently consisting of two redundant bits for checking
`that the message received is correct. Finally the trans(cid:173)
`mission line is released by the transmitting unit and the
`signal on transmission conductor 11 returns to the
`"high" resting level.
`A command from one of the slave units 27 to another
`(or several other) slave units 27 is transmitted via master
`unit 5 through steps which will be described w1th refer(cid:173)
`ence to FIG. 4 which shows their tempera! sequence.
`Assuming for example that at an initial instant 0 a pulse
`is activated from switch unit 14 on door 2 to cause the
`window winding device 18 in door 2' to open (FIG. 1),
`initially slave unit 27 (indicated by A) associated with
`this switch device 14 on door 2 decodes the type of
`activation made and ascertains that no communication
`is already in progress on the transmission line by check(cid:173)
`ing the voltage legvel in transmission conductor 11,
`which is at the high level when at rest as already de(cid:173)
`scribed. If the level is high at instant t1 (I msec) this
`slave unit 27 (A) transmits via transmission conductor
`11 a coded message of the type illustrated in FIG. 3
`containing its own identification code, the command
`code and the check field. At instant t2 (8 msec) the
`coded message is received by master unit 5, which may
`be "activated" by the first field 50 of this message to
`return to a fully operative condition from a resting stage
`of low power consumption in which it may be, and this
`master unit 5 checks that the message received is cor(cid:173)
`rect and that the corresponding command can be exe(cid:173)
`cuted. If this is the case, at instant t3 (9 msec) this master
`unit 5 transmits a coded message, again of the type
`illustrated in FIG. 3, including the identification code
`for the slave unit 27 (B), the command code and the
`check field, along transmission conductor 11' which
`passes to slave units 27 including the unit 27 (indicated
`by B in FIG. 1) associated with the window winding
`device 18 on door 2'. At instant t4 (15 msec), the coded
`message is recognised by that slave unit 27 (B), which
`checks that the message received is correct, and if this is
`the case causes the window winding device to be acti(cid:173)
`vated. From that instant t4 slave unit 27 (B) controls the
`occupation of transmission conductor 11' by means of a
`low logic level signal corresponding to an extension of
`field 50 in FIG. 3 for a sufficient time (t4-t5, conve(cid:173)
`niently 3 msec), to allow the disturbances due to the
`start-up of the actuator control by that unit 27 (B) to
`dampen down, and then at instant t5 (18 msec) that
`slave unit 27 (B) transmits a coded message to master
`unit 5 via transmission conductor 11' containing its own
`identification code, the code for the status of the actua(cid:173)
`tor controlled by that unit 27 (B), therefore indicating
`that implementation of the command has been acti(cid:173)
`vated, together with any diagnostic information, and
`the check field. At instant t6 (23 msec) the coded mes(cid:173)
`sage is received by master unit 5, which checks that the
`actuation has been correctly activated, at instant t7 (25
`msec) it transmits a coded message, again of the type
`
`Page 7
`
`

`

`5,121,386
`
`55
`
`5
`illustrated in FIG. 3, comprising the identification code
`of the slave unit 27 (A) and code confirming that the
`actuation command for the selective device of unit 27
`(B) has been transmitted (actuation in progress), along
`transmission conductor 11 which passes to slave units 5
`27 including unit 27 (A) associated with the switch
`activated by the control device 14. At instant t8 (31
`msec) the coded message is recognized by the slave unit
`27 (A), and on conclusion of the communication cycle
`described this can then return to the resting state after 10
`confirming that the command has been executed.
`In the event of a failure at any level of the chain in the
`abovementioned communication cycle, unit 27 or 5,
`which at that time is acting as a transmitter, on failing to
`receive replay messages or detect any activity on the 15
`transmission line, repeats the message for a finite num(cid:173)
`ber of times.
`The advantages obtained with the communication
`system according to this invention are obvious from
`what has been described.
`To begin with, the complexity of the transmission
`protocol and therefore the complexity of the slave units
`is very much reduced in comparison with a multimaster
`system. This makes it possible to use a smaller number
`of components to construct the said slave units (by way 25
`of indicating 10 to 60 in a local network), which is
`particularly advantageous for applications in motor
`vehicles, such as that described, where on account of
`mass production cost reductions are of major impor(cid:173)
`tance, and there is also a useful reduction in size en- 30
`abling the units to be mounted directly on the various
`electromechanical devices.
`Transmission can be initiated from any slave unit
`without having to have additional lines to request com(cid:173)
`munication. This is particularly advantageous in appli- 35
`cations in motor vehicles, like that described, where
`there must be a resting state in which overall minimum
`power consumption is guaranteed in order to avoid
`discharging the battery. In this state it is not possible to
`maintain an active master unit operating an interroga- 40
`tion or synchronization program as would be necessary
`with master/slave architecture. In the special applica(cid:173)
`tion described it is necessary to be able to release all the
`door locks simultaneously following the manual release
`of one of these when the system is in the low power 45
`consumption state (vehicle parked and completely at
`rest).
`There is a single master unit in which the pro(cid:173)
`grammed logic elements (e.g. The microprocessor) are
`concentrated. In general this assists the handling of all 50
`commands and/or enables for the functioning of vari(cid:173)
`ous actuators, with resulting simplicity, reliability and
`flexibility of the system, and the possibility of identify(cid:173)
`ing errors, in addition to the possibility of communicat(cid:173)
`ing with other intelligent systems.
`As all messages must be received and transmitted by
`the master unit (unlike multimaster systems) the latter
`can operate degraded functioning modes in the event of
`a local fault, if a particular arrangement is selected for
`the various communication lines, for example the "star" 60
`arrangement illustrated in FIG. 1, where a plurality of
`groups of slave units are connected to corresponding
`communication lines which are in turn connected to the
`master unit as described in the Italian patent application
`lodged on the same date by the same applicant entitled: 65
`"Connection system between a master unit and slave
`units", the contents of which are incorporated in this
`description by simple reference where necessary. This
`
`6
`may be done without recourse to duplicating the trans(cid:173)
`mission line, which in the specific application of motor
`vehicles is one of the most frequent causes of a fault.
`Other advantages are
`The structure of the communication message is ex(cid:173)
`tremely simple. Only a single constant identification
`field 51 for each slave unit 27, functioning as an address
`or signature for the message which the slave unit must
`receive or has sent.
`Data field 52 is reduced to a minimum (in fact, using
`only four bits, movement can be controlled in three
`axes, plus a power actuation for a given actuator, for
`example that of device 15 which electrically controls
`outside rear-view mirror 16), as there are no different
`possible interpretations of the data.
`The structure of such a message makes it possible to
`activate any one of the units connected to the communi(cid:173)
`cation line from a resting condition whenever such a
`message is initiated, this being determined by the initial
`20 low level field 50, and to return to the low power con(cid:173)
`sumption resting condition when the communication
`line is again free (detected by the high level logic signal
`for a predetermined time).
`The structure of the communication may be handled
`simultaneously with communication structured in a
`different way, for example:
`a) it may coexist with cyclical interrogation (polling)
`of the slave units by the master unit, merely by
`authorising the latter to perform this function only
`after a period of time during which the communi(cid:173)
`cation line is free for a period longer than that
`specified for command transmissions in real time.
`b) the master unit may under certain conditions be(cid:173)
`come transparent, allowing the possibility of direct
`transmission between slave units, or
`c) given the possibility of using a "star" connection
`arrangement centered on the ma'Ster unit as de(cid:173)
`scribed,
`any non-functioning
`communication
`branches can be isolated.
`Finally, it is clear that modifications and variants may
`be applied to the embodiment of this invention de(cid:173)
`scribed and illustrated without going beyond the scope
`of the inventive concept contained within it. For exam(cid:173)
`ple the number and allocation of the connected devices
`indicated by way of example may be varied and the
`circuit configurations which have been illustrated by
`way of example in the diagrams may also be varied. In
`addition to this master unit 5 may have connections
`between the various communication conductors 11, 11',
`11", ... , other than those illustrated in FIG. 2, with
`communication interconnections as described in the
`abovementioned patent application entitled: "Connec(cid:173)
`tion system between a master unit and slave units".
`We claim:
`1. A connection system between at least one master
`unit and a plurality of slave units, comprising:
`a communication channel directly connected to said
`plurality of slave units and to said master unit, each
`slave unit of said plurality of slave units including
`logic means for exchanging communication mes(cid:173)
`sages with said master unit and for independently
`initiating transmission toward said master unit, said
`communication message has a preliminary field
`which can be used to activate said master and slave
`units from a resting state of minimum power con(cid:173)
`sumption;
`said slave and master units are connected to said
`communication channel by means which force said
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`5,121,386
`
`10
`
`35
`
`25
`
`7
`communication channel to a different logical level
`when said communication channel is occupied by
`one of said master and slave units in order to send
`said communication message, said master and slave
`units detecting that said communication channel is 5
`in a free condition for the forwarding of said com(cid:173)
`munication message by means for detecting said
`different logical level of said communication chan(cid:173)
`nel; and
`said master unit including means for receiving said
`communication message from one of said plurality
`of slave units and for sensing said communication
`message to another of said plurality of slave units.
`2. A system according to claim 1, wherein said com(cid:173)
`munication messages exchanged by said slave units with
`said master unit comprise a first field identifying a said 15
`slave unit and a second data field.
`3. A system according to claim 2, wherein said first
`field identifies said slave unit which sent said communi(cid:173)
`cation in the event of transmission towards said master
`unit and identifies said slave unit which is to receive said 20
`communication in the case of transmission towards said
`slave unit.
`4. A system according to claim 2, said second data
`field includes activation or control data for said slave
`unit and said master unit.
`5. A system according to claim 2, wherein said first
`field consists of six bits and said second field consists of
`four bits.
`6. A system according to claim 1, wherein said logical
`means include at least one data receipt means for detect- 30
`ing data signals on said communication channel, and at
`least one transmitting means for transmitting data sig(cid:173)
`nals on said communication channel.
`7. A system according to claim 1, wherein transmis(cid:173)
`sion of said communication message is effected by
`means of an asynchronous serial protocol.
`8. A system according to claim 7, wherein said trans(cid:173)
`mission is effectuated by constant pulse height duration
`modulation.
`9. A system according to claim 1, comprising groups
`of said slave units connected to corresponding commu- 40
`nication lines connected to said master unit.
`10. A system according to claim 9 wherein the num(cid:173)
`ber of said slave units in each of said groups of slave
`units is ten.
`11. A system according to claim 9, wherein said mas- 45
`ter unit includes means for controlling the exchange of
`data signals between said communication lines.
`12. A system according to claim 1, wherein said mas(cid:173)
`ter unit includes a microprocessor.
`13. A system according to claim 1, wherein said slave so
`units are associated with electrical devices in a vehicle
`for activating or controlling at least one electrically
`functioning member in said electrical devices.
`14. A system according to claim 13, comprising a first
`of said slave units is by means of said logical means 55
`capable of sending to said master unit a first communi(cid:173)
`cation message to actuate one of said electrical devices
`controlled by a second of said slave units, said master
`unit is capable of sending a second actuation command
`message for said second of said slave units, said second
`slave unit is capable of sending to said master unit a 60
`third message providing information about said actua(cid:173)
`tion, and that said master unit is capable of sending to
`said first slave unit a fourth message confirming receipt
`of the actuation command from said second slave unit.
`15. A system according to claim 13, wherein said 65
`slave units include at least one integrated circuit provid(cid:173)
`ing means for the distribution of electrical power for
`operation of said electrical devices, and means for the
`
`8
`treatment of data signals relating to the functioning of
`said electrical devices.
`16. A system according to claim 1. wherein said com(cid:173)
`munication channel between said slave units and said
`master unit is provided by means of at least one electri(cid:173)
`cal connection cable comprising a first conductor with
`a positive electrical power supply, a second conductor
`for the transmission of data signals and a third conduc(cid:173)
`tor which is connected to ground.
`17. A system according to claim 16, wherein said at
`least one electrical connection cable includes a single
`one of said electrical connection cable for at least the
`said electrical devices associated with one door of a
`vehicle.
`18. A system according to claim 17, wherein said
`devices associated with said one door include at least
`one window winding device, a door locking device and
`a manual control switch device.
`19. A system according to claim 18, wherein said
`electrical devices associated with said one door also
`include an electrical device for electrical control of an
`outside rear-view mirror.
`20. The system according to claim 1, wherein said
`preliminary field products a different logical level in
`said communication channel.
`21. A connection system between at least one master
`unit and a plurality of slave units, comprising:
`a communication channel directly connected to said
`plurality of slave units and to said master unit, each
`slave unit of said plurality of slave units including
`logic means for exchanging communication mes(cid:173)
`sages with said master unit and for independently
`initiating transmission toward said master unit, said
`slave units are associated with electrical devices in
`a vehicle for activating or controlling at least one
`electrically functioning member in said electrical
`devices; and
`said system further comprising a first of said slave
`units being by means of said logical means capable
`of sending to said master unit a first communication
`message to actuate one of said electrical devices
`controlled by a second of said slave units, said
`master unit is capable of sending a second actuation
`command message for said second of said slave
`units, said second slave unit is capable of sending to
`said master unit a third message providing informa(cid:173)
`tion about said actuation, and that said master unit
`is capable of sending of said first slave unit a fourth
`message confirming receipt of the actuation com(cid:173)
`mand from said second slave unit.
`22. A system according to claim 21 wherein said slave
`and master units are connected to said communication
`channel by means which force the said communication
`channel to a different logical level when said communi(cid:173)
`cation channel is occupied by one of said master and
`slave units in order to send said communication mes(cid:173)
`sage.
`23. A system according to claim 22, wherein said
`master and slave units detect that said communication
`channel is in a free condition for the forwarding of said
`communication message by means for detecting said
`different logical level of said communication channel.
`24. A system according to claim 23, wherein said
`communication message h