WO2004105277A1

WO2004105277A1 - Method and system for transmission of digital data between a master device and a slave device

Info

Publication number: WO2004105277A1
Application number: PCT/FR2004/001274
Authority: WO
Inventors: Vincent Brient
Original assignee: Wavecom
Priority date: 2003-05-19
Filing date: 2004-05-19
Publication date: 2004-12-02
Also published as: FR2855347B1; FR2855347A1

Abstract

The invention relates to a method for transmission of digital data between a master device and a slave device, the transmitted data comprising audio data and signalling and/or control data, whereby the master device generates an audio clock bit and an audio sampling clock. According to the invention, the data are transmitted in synchronous frames, each comprising a preamble and an effective portion, the effective portion of each frame comprising at least one audio data field and at least one signaling and/or control data field. The preamble is transmitted by the master device at the frequency of the audio clock bit and have a predetermined structure, such that the slave device detects the preamble and can determine the audio clock bit.

Description

Method and system for transmitting digital data between a master device and a slave device

The field of the invention is that of the transmission of digital data. More specifically, the invention relates to a method and a system for transmitting digital data between a master device and a slave device, in the case where the transmitted data include audio data and signaling and / or control data. It is also assumed that the master device generates an audio bit clock and an audio sampling clock. In a particular application of the invention related to radiocommunication, we are interested in the transmission of digital data between a master device comprising a radiocommunication module allowing access to a radiocommunication network and a slave device comprising means of use and / or control of the radiocommunication module. It will be recalled that the radiocommunication module is an essential element of a radiotelephone. Usually (first application), the radiocommunication module is included in a radiocommunication terminal which cooperates with a subscriber identification module (or SIM card, for "Subscriber Identity Module" in English). Other applications have already been envisaged for the above-mentioned radiocommunication module. It has in particular been proposed (second application) to integrate the radiocommunication module into devices other than radiocommunication terminals, but nevertheless requiring wireless communication functionality. By way of example, mention may be made of telemetry devices (meter readings), alarm devices or even bank card reader devices. It has also been proposed (third application) to provide the radiocommunication module in independent form: it is then qualified as a modem. Such a modem does not include any hardware (screen, keyboard, speaker, etc.) for the man / machine interface. It is intended to cooperate with third-party equipment which has human / machine interface hardware elements. Third-party equipment may in particular, but not exclusively, be a microcomputer. Furthermore, by means of use and / or control of the radiocommunication module, we mean in particular but not exclusively: a screen, a keyboard, a speaker, a hands-free kit, third-party equipment (microcomputer, personal digital assistant (PDA), navigation device (for example GPS type), etc.

In the application of the present invention linked to radiocommunication, the digital audio data are for example GSM audio data (generated directly by the radiocommunication module or by means of an audio codec placed at the output of the radiocommunication module) . The signaling and / or control data includes, for example: data from a bidirectional asynchronous serial port of the UART (“Universal Asynchronous Receiver / Transmitter”) type, dedicated to third-party equipment and enabling the radio module to be controlled by this third-party equipment (for example by AT commands), the transfer to the third-party equipment of data coming from the network and received by the radiocommunication module as a modem,

..., data from a UART type unidirectional serial port, dedicated to a navigation device; data representing the state of a plurality of generic input / output signals, also called GPIO signals (“General Purposes Input / Output”), each relating to a particular function (for example the flashing of a light-emitting diode (OF THE)) ; data representing the state of a plurality of control signals of the aforementioned asynchronous bidirectional serial port.

The application linked to radiocommunication can be envisaged in several contexts. For example, in a first context, the master device is located in the trunk of a motor vehicle and the slave device in the dashboard area of this vehicle. In a second context, the master device is located outside of an elevator car and the slave device inside this elevator car. It is clear that many other applications, whether or not related to the field of radiocommunication, can be envisaged without departing from the scope of the present invention.

By way of illustration and for the sake of simplification, the technique of the prior art and its drawbacks are now presented in relation to the first aforementioned context of the particular application of the invention related to radiocommunication.

The current technique consists in making a ribbon cable, so that the data transmission is carried out in parallel on a plurality of cables. Thus, for example: two wires are used to transmit GSM audio data: one for transmission from the radiocommunication module to the loudspeaker or the hands-free kit, the other for transmission from the microphone or the hands-free kit to the radiocommunication module; two wires to transmit data from the asynchronous bidirectional serial port dedicated to third-party equipment; a wire for transmitting data from a unidirectional serial port, dedicated to a navigation device; a plurality of wires (e.g. eight) for transmitting data representing the state of a plurality of GPIO signals. This current technique has several drawbacks. First of all, ribbon cabling is complex, expensive and has a large footprint. Furthermore, because of the plurality of wires, problems arise in terms of electromagnetic compatibility and operation, in particular for the audio data which are the most sensitive to noise. It has also been proposed, in other contexts, to replace ribbon cable with a CAN (“Controller Area Network”) bus. The CAN bus is a serial bus used to connect a plurality of control units.

Typically, in a car, two CAN buses are used. One, called high speed CAN bus (up to 1 Mb / s), allows the interconnection of control units relating to the following elements or functions: dashboard, engine, braking (anti-lock), active suspension, transmission, etc. The other, said low speed CAN bus (up to 125 kb / s), allows the interconnection of control units relating to the following elements or functions: dashboard, lighting, air conditioning, airbags, door locks, electric windows, etc.

Each CAN bus implements a protocol of the same name (CAN protocol) which is a serial communication protocol which supports real time systems with a high level of reliability in a limited and severe environment such as a factory, a workshop, a car. .. The CAN protocol covers two of the seven layers of the ISO OSI Open Systems Interconnection Model, namely the physical layer (layer 1) and the data link layer (layer 2). For more information on the CAN bus, reference can be made to the ISO 11898 standard, inserted here by reference.

The CAN protocol data link layer is such that each control unit can send and receive data. The data is conveyed on the bus in the form of asynchronous packets (frames) of defined format but of variable and limited length. As soon as the bus is free, any control unit connected to the bus can send a new packet. An interruption mechanism for higher priority packets is provided, as well as a mechanism for arbitrating conflicts resulting from the simultaneous transmission of several packets on the bus when it is free.

The question can be asked whether the CAN bus can be used in the context of the present invention, that is to say by assuming that the master device and the slave device each constitute a control unit connected to the same CAN bus.

The negative answer should be that the data link layer of the CAN protocol is not suitable for the transmission of audio data and signaling and / or control data. Indeed, the asynchronous nature of the packets (frames) conveyed by the CAN bus is not suitable for audio data since it does not guarantee a constant instantaneous bit rate.

It is not possible to remedy this problem by using FIFO type buffer memories to store the packets and restore them at a suitable constant rate. Indeed, such a solution would not be suitable because it would introduce an annoying delay, especially for the echo canceller ("echo canceller"). In addition, it is difficult to produce FIFO memories whose input speed is not constant (here imposed by the speed of arrival of asynchronous packets on the CAN bus) and whose output speed is constant.

The reconstruction of the audio bit clock by implementing a phase locked loop (PLL) by the slave device is also not a satisfactory solution. Indeed, it is a complex and expensive solution.

The object of the invention is in particular to overcome these various drawbacks of the state of the art.

More specifically, one of the objectives of the present invention is to provide a method and a system for transmitting digital data making it possible, in the aforementioned context, to simplify the wiring and to avoid ribbon wiring.

The invention also aims to provide such a method and system suitable for the simultaneous transmission of audio data and signaling and / or control data.

Another objective of the invention is to provide such a method and system that does not require FIFO type buffer memories, nor a phase locked loop.

(PLL).

A complementary objective of the invention is to provide such a method and system making it possible to benefit from all the advantages linked to the physical layer (layer

1) CAN protocol. These various objectives, as well as others which will appear subsequently, are achieved according to the invention using a method of transmitting digital data between a master device and a slave device, the transmitted data comprising audio data. and signaling and / or control data, the master device generating an audio bit clock and an audio sampling clock. The data are transmitted in synchronous frames each comprising a preamble and a useful part, the useful part of each frame comprising at least one audio data field and at least one signaling and / or control data field, the preambles being transmitted. by the master device at the frequency of the audio bit clock and having a predetermined structure, so that the slave device detects the preambles and covers the audio bit clock. The general principle of the invention therefore consists in multiplexing audio data and signaling and / or control data in synchronous frames transmitted at the rate of the audio bit clock (and thus transporting this audio bit clock).

The wiring is very simple since the transmission is carried out on a single cable.

The present invention is all the more advantageous when the number of signaling and / or control data contained in the useful part of a frame is high, which implies that the signaling and / or control data have a high bit rate. with respect to the bit rate of the audio data (since, for a given direction of transmission, there is only one bit of audio data per frame). In other words, the efficiency is improved if the number of bits of preambles transmitted remains low compared to the number of bits of useful parts transmitted (audio data and signaling and / or control data).

In a particular embodiment of the invention, the useful part of each frame comprises: - at least one first audio data field, used for the transmission of audio data from the master device to the slave device; at least one second audio data field, used for the transmission of audio data from the slave device to the master device. Thus, in this particular embodiment, the transmission of the audio data is bidirectional. It is clear however that the invention also relates to the case where the transmission of audio data is unidirectional (from the master device to the slave device, or vice versa).

Advantageously, the master device transmits at least a first and a second type of preamble. The second type of preamble is used only for one frame every M frames, with M the ratio between the frequency of the audio bit clock and the frequency of the audio sampling clock, so that the slave device detects the preambles of the second type and overlays the audio sampling clock.

Thus, the frames also carry the audio sampling clock. According to an advantageous variant, the useful part of each frame comprises a first signaling and / or control data field which may contain a first or second information. The first signaling and / or control data field contains the second information for a frame every M frames, with M the ratio between the frequency of the audio bit clock and the frequency of the audio sampling clock, from so that the slave device detects the first signaling and / or control data fields containing the second information and covers the audio sampling clock.

Again, the frames also carry the audio sampling clock. Advantageously, the useful part of each frame comprises at least a second signaling and / or control data field in which are temporally multiplexed, according to a pattern of M successive frames, data relating to the state of P signaling signals and / or control, with P ≤ M, said at least one second signaling and / or control data field being used, for each row of the pattern of M successive frames, in a predetermined manner either for the transmission of data from the device master to the slave device, i.e. for data transmission from the slave device to the master device.

According to an advantageous characteristic, the useful part of each frame comprises at least a third signaling and / or control data field in which data relating to the state of a first serial signaling and / or control port are transmitted. , said at least one third signaling and / or control data field being used in a predetermined manner either for the transmission of data from the master device to the slave device, or for the transmission of data from the slave device to the master device .

Advantageously, the master device transmits at least a third and a fourth type of preamble. The useful part of each frame comprises at least a fourth signaling and / or control data field in which data relating to the state of a transmission channel of a second signaling serial port and / or are transmitted. control, said at least one fourth signaling and / or control data field being used for the transmission of data from the master device to the slave device. The fourth type of preamble is used after the master device has detected a start bit on the transmit channel of the second serial port, the fourth type of preamble indicating that the eight bits consecutive carried by the fourth or more signaling and / or control data field (s) carry a byte of the transmission channel of the second serial port, so that the slave device detects the preambles of the fourth type and generates bytes, each preceded by a start bit, in the format of the second serial port. According to an advantageous variant, the useful part of each frame comprises at least a fourth signaling and / or control data field in which data relating to the state of a transmission channel of a second serial port are transmitted signaling and / or control, said at least one fourth signaling and / or control data field being used for the transmission of data from the master device to the slave device. The useful part of each frame includes a fifth signaling and / or control data field which may contain third or fourth information. The fifth signaling and / or control data field contains the fourth information if the master device has detected a start bit on the transmission channel of the second serial port, the fourth information indicating that the eight consecutive bits carried by the or the fourth signaling and / or control data field (s) carry a byte of the transmission channel of the second serial port, so that the slave device detects the fifth signaling and / or control data field containing the fourth information, and generates bytes, each preceded by a start bit, in the format of the second serial port.

Compared to the aforementioned embodiment, this variant requires the use of a fifth field of signaling and / or control data, which reduces the space available in the useful part for the transmission of other signaling data and / or control. Advantageously, the useful part of each frame comprises at least two fourth signaling and / or control data fields which are approximately half the length of said frame, so that the slave device can process the contents of each of the fourth signaling and / or control data fields. Preferably, the size of the set or all of the fourth field (s) of signaling and / or control data is such that the bit rate which it (s) carries (s) is sufficient so that neither the master device nor the slave device has to memorize in full each byte of the transmission channel of the second serial port.

Advantageously, the master device transmits at least a fifth and a sixth type of preamble. The useful part of each frame comprises at least a sixth signaling and / or control data field in which data relating to the state of a reception channel of a second signaling and / or serial port are transmitted. control, said at least one sixth signaling and / or control data field being used for the transmission of data from the slave device to the master device. The sixth type of preamble is used after the slave device has detected a start bit on the reception channel of the second serial port, the sixth type of preamble indicating that the eight consecutive bits carried by the sixth field (s) ( s) signaling and / or control data transport a byte of the reception channel of the second serial port, so that the master device detects the preambles of the sixth type and generates bytes, each preceded by a start bit, at the format of the second serial port.

According to an advantageous variant, the useful part of each frame comprises at least a sixth signaling and / or control data field in which are transmitted data relating to the state of a reception channel of a second serial port of signaling and / or control, said at least one sixth signaling and / or control data field being used for the transmission of data from the slave device to the master device. The useful part of each frame includes a seventh signaling and / or control data field which may contain fifth or sixth information. The seventh signaling and / or control data field contains the sixth information if the slave device has detected a start bit on the reception channel of the second serial port, the sixth information indicating that the eight consecutive bits carried by the one or more sixth signaling and / or control data field (s) carry one byte of the reception channel of the second serial port, so that the master device detects the seventh signaling and / or control data field containing the sixth information, and generates bytes, each preceded by a start bit, in the format of the second serial port. Compared to the aforementioned embodiment, this variant requires the use of a seventh signaling and / or control data field, which reduces the space available in the useful part for the transmission of other signaling data and / or control. Advantageously, the useful part of each frame comprises at least two sixth fields of signaling and / or control data distant from approximately half the length of said frame, so that the master device can process the contents of each of the sixth signaling and / or control data fields. Preferably, the size of or all of the sixth field (s) of signaling and / or control data is such that the bit rate which it (s) carries (s) is sufficient so that neither the device neither the master nor the slave device has to memorize in full each byte of the reception channel of the second serial port.

Preferably, the preamble has two rising or falling edges separated by a predetermined number NI of clock strokes of a reference clock, such as:

NI ≠ N2, with N2 = k.N, k being an integer greater than or equal to one, N being the number of strokes of the reference clock used for each bit of the useful part of each frame; - NI ≠ N3, with N3 the number of strokes of the reference clock separating the last rising or falling edge inside the useful part of the previous frame and the first rising or falling edge at inside the preamble of the current frame;

NI ≠ N4, with N4 the number of strokes of the reference clock separating the last rising edge, or falling edge, inside the preamble of the current frame and the first rising edge, or falling edge, inside the useful part of the current frame.

In a particular embodiment of the invention, NI = 12, N3 = N4 = 18 and N = 8. In an advantageous embodiment of the invention, the frequency of the audio bit clock is 64 kHz, and the audio sampling clock frequency is 8 kHz. Preferably, the data is transmitted between the master device and the slave device on a medium conforming to the physical layer of the CAN bus protocol.

Thus, the method according to the invention benefits from all the advantages linked to the physical layer (layer 1) of the CAN protocol. In this case, the method of the invention can be seen as a digital data transmission protocol covering the data link layer (layer 2) and replacing the CAN protocol (which is not adapted to it for data transmission. audio, see discussion above). It is recalled that the physical layer of the CAN protocol is based on a “wired-AND” (“wired-AND”) bus architecture with the use of CAN specific analog transmitter / receiver circuits and also CAN specific connectors. It guarantees electromagnetic isolation (EMI) and low consumption.

The invention also relates to an application of the above method to the transmission of digital data between: - a master device comprising a radiocommunication module allowing access to a radiocommunication network and a slave device comprising means of use and / or of radio module control.

Advantageously, the master device is located in a first part of a motor vehicle, preferably a trunk, and the slave device is located in a second part of said motor vehicle, preferably a dashboard.

According to an advantageous variant, the master device is located outside of an elevator car and the slave device is located inside said elevator car. It is clear that many other applications can be envisaged without departing from the scope of the present invention.

The invention also relates to a system for transmitting digital data between a master device and a slave device, the transmitted data comprising audio data and signaling and / or control data, the master device generating an audio bit clock and a clock. audio sampling.

The master device includes: means for generating synchronous frames in which the data are transmitted and each comprising a preamble and a useful part, the useful part of each frame comprising at least one audio data field and at least one signaling and / or signal data field control; means for transmitting the preambles at the frequency of the audio bit clock and with a predetermined structure.

The slave device comprises: means for detecting preambles; means for recovering the audio bit clock. The invention also relates to a signal transporting digital data between a master device and a slave device, the transported data comprising audio data and signaling and / or control data, the master device generating an audio bit clock and a clock. audio sampling. This signal has a structure with synchronous frames each comprising a preamble and a useful part, the useful part of each frame comprising at least one audio data field and at least one signaling and / or control data field, the preambles being emitted by the master device at the frequency of the audio bit clock and having a predetermined structure, so that the slave device detects the preambles and covers the audio bit clock. Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of non-limiting example, and the accompanying drawings, in which: Figure 1 shows a block diagram of a particular embodiment of the system according to the invention; FIG. 2 shows an example of a sequence of frames in which digital data are exchanged between the master device and the slave device appearing in FIG. 1, as well as the audio bit clock and the audio sampling clock transported by these frames; FIG. 3 shows a particular embodiment of the structure of a preamble of a frame; FIG. 4 shows a particular embodiment of the structure of the useful part of a frame.

The invention therefore relates to a method and a system for transmitting digital data between a master device and a slave device. The general principle consists in multiplexing audio data and signaling and / or control data in synchronous frames transmitted at the rate of an audio bit clock generated by the master device.

In the particular embodiment described below by way of example, we present a particular application mentioned above related to radiocommunication. The master device is for example located in the trunk of a motor vehicle, and the slave device at the dashboard of this vehicle. Alternatively, the master device is located outside of an elevator car and the slave device inside this elevator car. Many other variants can of course be envisaged without departing from the scope of the present invention. As illustrated in the block diagram of FIG. 1. the master device 1 and the slave device 2 are connected by a CAN cable (or bus) 3, that is to say a cable on which the physical layer can be implemented (layer 1) of the CAN protocol (see standard ISO 11898). Thus, in the case of a vehicle in which two CAN buses are already used (CAN bus at high and low speeds respectively), the invention is implemented on a third bus.

It will be recalled that the invention can be seen as a new data transmission protocol covering, like the CAN protocol, the physical layer (layer 1) and the data link layer (layer 2) of the OSI open systems interconnection model. of ISO. The physical layer of this new protocol is for example identical to that of the CAN protocol. On the other hand, the data link layer of this new protocol is different from that of the CAN protocol, in that it is suitable for the transmission of audio data. The master device 1 comprises: a radiocommunication module 4 (conforming to the GSM standard for example) allowing access to a radiocommunication network (not shown); a first audio coded 5, transforming bidirectional analog audio signals (on two wires), present at the input / output of the radiocommunication module 4, into bidirectional digital audio data (at 64 kb / s in each direction), and vice versa; a first multiplexer / demultiplexer 6 transforming the bidirectional digital audio data present at the input / output of the first coded audio 5, as well as signaling and / or control data present at the input / output of the radiocommunication module 4, into a multiplex of digital data at 1 Mb / s, and vice versa. As explained in detail below, in relation to FIGS. 2 to 4, this multiplex is conveyed in synchronous frames; an interface component 7 specialized for the physical layer of the CAN protocol, and constituting a CAN specific analog transmitter / receiver circuit, between the first multiplexer / demultiplexer 6 and the CAN cable 3; means for generating an audio bit clock (at 64 kHz in the particular embodiment described here); means for generating an audio sampling clock (at 8 kHz in the particular embodiment described here); - means for generating a bit clock for transport on the bus

CAN (at 1.024 MHz in the particular embodiment described here). In an alternative embodiment, the first audio codec 5 can be integrated into the radiocommunication module 4, or even omitted if the radiocommunication module 4 receives audio data already in digital form from the network. In the example illustrated in FIG. 1, the signaling and / or control data comprise: data relating to the state of the transmission and reception channels (on two wires) of an asynchronous bidirectional serial port of the type UART (hereinafter called "UART1 serial port"). This serial port UART1 has for example a signaling and / or control data rate of 115.2 kb / s on each channel. It is dedicated to third-party equipment 13. It allows name the control of the radiocommunication module 4 by this third-party equipment 13 (thanks for example to AT commands), as well as the transfer to this third-party equipment 13 of data coming from the network and received by the radiocommunication module 4 as a modem ( operation in GPRS mode); data relating to the state of the transmission channel (on a wire) of a unidirectional serial port of UART type (hereinafter called "GPS serial port"), dedicated to a navigation device 14 (for example according to the GPS standard). This GPS serial port has for example a signaling and / or control data rate of 4.8 kb / s; data relating to the state of a plurality of generic input / output signals (hereinafter called "GPIO signals") (on a plurality of wires) each relating to a particular function; data relating to the state of a plurality of UART1 serial port control signals (hereinafter called "UART1 control signals") (on a plurality of wires). positive slave 2 includes: a second interface component 8 identical to the first (referenced 7) included in the master device 1. It constitutes a CAN specific analog transmitter / receiver circuit, between the CAN cable 3 and a second multiplexer / demultiplexer 9 ( see below) ; a second multiplexer / demultiplexer 9, transforming the 1 Mb / s digital data multiplex, present at the input / output of the second interface component 8, into bidirectional digital audio data (at 64 kb / s in each direction), thus that signaling and / or control data (with the same distribution in substream as that existing in input / output of the radiocommunication module 4), and vice versa; a second coded audio (hands-free kit) 10, transforming the bidirectional digital audio data, present at the input / output of the second multiplexer / demultiplexer 9, into bidirectional analog audio signals (on two wires), and vice versa; a loudspeaker 11 cooperating with an amplifier (not shown) and receiving (on a wire) the analog audio signals leaving the second audio codec 10; a microphone 12 cooperating with an amplifier (not shown) and transmitting (on a wire) the analog audio signals entering the second coded audio 10; the third-party equipment item 13 already discussed above, which exchanges with the second multiplexer / demultiplexer 9 the data relating to the state of the transmission and reception channels (on two wires) of the asynchronous bidirectional serial port UART1. In other words, the third party equipment 13 receives data coming from the serial port UART1 and transmits data to this serial port UART1, with a bit rate equal to 115.2 kb / s in both directions; - The navigation device 14 already discussed above, which receives from the second multiplexer / demultiplexer 9 the data relating to the state of the transmission channel (on a wire) of the unidirectional serial port GPS. In other words, the navigation device 14 receives data coming from the GPS serial port, with a bit rate equal to 4.8 kb / s; a plurality of elements (symbolized by the square referenced 15), each exchanging with the second multiplexer / demultiplexer 9 (on a wire and in a predetermined direction, transmission or reception) the data relating to the state of one of GPIO signals or one of the UART1 control signals. One of the elements 15 is for example a light-emitting diode (LED), the flashing of which depends on the state of one of the GPIO signals.

FIG. 2 shows an example of a sequence of synchronous frames, referenced T1 to T16, in which digital data are exchanged between the master device 1 and the slave device 2. The audio bit clock (64 kHz) and the clock audio sampling (8 kHz), generated by master device 1, are also shown. The frames are constructed and processed by the first and second multiplexers / demultiplexers 6, 9, included in the master device 1 and the slave device 2 respectively.

They each include a preamble and a useful part, and have for example a total length of 16 bits (4 for the preamble and 12 for the useful part).

In this case, the frequency of the bit clock for transport on the CAN bus is equal to 1.024 MHz (= 16 x 64 kHz, with 64 kHz the frequency of the bit audio clock). This value (1.024 MHz), because it is sufficiently close to the standard bit rate (1 Mb / s) provided on a conventional CAN bus, is compatible with the radiation and electromagnetic compatibility tests carried out as part of the standardization of the physical layer of the CAN protocol.

The preambles are sent by the master device 1 (and more precisely by the first multiplexer / demultiplexer 6) at the frequency of the audio bit clock (64 kHz). They have a predetermined structure, so that the slave device 2 detects them and covers the audio bit clock.

We now present, in relation to FIG. 3, a particular embodiment of the structure of a frame preamble.

A reference clock at 8.192 MHz, that is to say eight times faster than the bit clock, is used for transport on the CAN bus (at 1.024 MHz). Thus, each data bit transmitted on the CAN bus has a length N of 8 cycles of the reference clock.

The preamble P has a length of 32 cycles of the reference clock, successively: 10 cycles at the low level, 6 at the high level, 6 at the low level and 10 at the high level. Thus, the slave device 2 (and more precisely the second multiplexer / demultiplexer 9) detects a preamble when it measures 12 cycles between two rising edges.

Indeed, this number of cycles (12) is such that:

12 ≠ N2, with N2 = k.N, k being an integer greater than or equal to one, N (= 8) being the number of cycles of the reference clock used for each bit of data in the useful part of each frame;

12 ≠ 18, with 18: * the number N3 of cycles of the reference clock separating the last rising edge inside the useful part of the previous frame and the first rising edge inside the preamble of the current frame;

* the number N4 of cycles of the reference clock separating the last rising edge inside the preamble of the current frame and the first rising edge inside the useful part of the current frame. In a variant, the preamble is reversed with respect to the preamble P presented above. It then successively includes: 10 cycles at the high level, 6 at the low level, 6 at the high level and 10 at the low level. In this case, the slave device 2 detects a preamble when it measures 12 cycles between two falling edges.

We now present, in relation to FIG. 4, a particular embodiment of the structure of the useful part 41 of a frame 40. It will be recalled that the useful part 41 of a current frame 40 is between the preamble 42 of this current frame 40 and the preamble 43 of the following frame. In this particular embodiment, the useful part comprises twelve data fields, referenced 51 to 512. Each of these fields, which has a length of one bit, is described in detail below.

The “audio synchro” field 51 takes the value “1” for one frame in eight (see in FIG. 2 the frames whose useful part is grayed out), and the value “0” for the other frames. It therefore changes value at the frequency of 8 kHz (= 64 kHz 8), that is to say the frequency of the audio sampling clock. The slave device 2 detects these changes in value, which each indicate a rising edge of the audio sampling clock. It can therefore recover the audio sampling clock. Once the slave device 2 has received the audio synchronization, that is to say has recovered the audio sampling clock, it numbers from one to eight all the frames it receives.

In an alternative embodiment of the invention, the “audio synchro” field can be deleted if a different preamble is sent every eight frames to indicate a rising edge of the audio sampling clock.

The “Audio TX data” field 59 contains a bit of outgoing audio data (from the master device to the slave device) and the “Audio RX data” field 510 contains an incoming audio data bit (from the slave device to the master device). We therefore have a duplex audio signal at 64 kb / s.

Depending on the number one to eight of the frame, the "GPIO data" field 58 represents the state of one of the eight GPIOs signals. The direction, input or output, for each GPIO signal is determined at the design of the system.

The “UART1 Ctrl data” field 57 functions in the same way as the “GPIO data” field 58, but is dedicated to the control signals of the UART1 serial port (each of these signals are well known to those skilled in the art and are not therefore not detailed here). The “GPS TX” field 56 contains a data bit relating to the state of the GPS serial port, independently of the number of the frame in which we are located. Indeed, the GPS serial port is a slow serial port (4.8 kHz) compared to the frame rate (64 kHz). To keep it simple, we can therefore simply sample the signal from the GPS serial port at 64 kHz. One thus obtains more than ten sampling points per bit of data, which is enough to faithfully reconstruct this signal. The UART1 serial port is an asynchronous serial port at 115,200 baud. It is therefore too fast to be sampled like the GPS port.

Therefore, in reception (from the slave device to the master device), the “UART1 RX synchro” field 54 is used. After detection by the slave device of a start bit “START” (which precedes a data byte) on the UART1 serial port reception channel, the data bit contained in the "UART1 RX synchro" field changes from "0" to "1" and thus indicates to the master device that the eight consecutive bits carried by the "UART1 RX datai" fields 55 and “UART1 RX data2” 512 will transport the data byte intended for the reception channel of port UART1. This byte is therefore transported at 128 kHz (= 2 x 64 kHz), while the serial port UART1 operates at 115.2 kHz on reception. The slave device must therefore wait until it has memorized two bits of this byte before starting to send it. It is interesting that the slave device does not have to memorize the entire byte, this makes it possible to implement the protocol of the invention, in the second multiplexer / demultiplexer 9 included in the slave device 2, in a programmable component of small size (eg CPLD type) and therefore inexpensive. When it receives and detects a “UART1 RX synchro” field containing the value

"1", the master device triggers the production of a start bit "START" then the bits forming the byte transported are immediately encoded in a serial port format at 115,200 Bauds, avoiding (this time on the master device side) any costly storage in memory. After the end of the sending of this byte, and as long as the bit of the field "UARTl RX synchro" does not return to "1", the fields "UARTl RX datai" and "UARTl RX data2" are unused.

In an alternative embodiment of the invention, the “UARTl RX synchro” field 54 can be deleted if a different preamble is sent to indicate that the eight consecutive bits carried by the “UARTl RX datai” and “UARTl RX data2” fields will carry the data byte. It should be noted that four types of preamble must be used if one wishes to combine the two variants mentioned above, that is to say if one wishes to delete the "audio synchro" field 51 and the "UARTl RX synchro" field. 54.

In transmission (from the master device to the slave device), the fields "UARTl TX synchro" 52, "UARTl TX datai" 53 and "UARTl RX data2" 511 are used. Their operation is similar to that of the fields "UARTl RX synchro" 54

“UARTl RX datai” 55 and “UARTl RX data2” 512 discussed above, the data going in the other direction and the roles of the master 1 and slave 2 devices being reversed.

It is clear that many other embodiments of the invention can be envisaged. One can in particular provide that the SIM card (or more generally the subscriber identification module) with which the radiocommunication module cooperates is also remote, that is to say included in the slave device (like the loudspeaker 11, microphone 12, third party equipment 13, navigation device 14, etc.). Thus, in the aforementioned example related to the automotive field, the SIM card is placed at the dashboard (and no longer in the trunk), so as to make it easier to change the SIM card.

The SIM card can in this case be seen as a half-duplex serial port, the data is therefore incoming or outgoing but not both at the same time. We can therefore use the same organization as that described for the UARTl serial port, but this time for a speed of 57,600 baud (instead of 115,200 baud) in a given direction. The frame includes “SIM synchro” and “SIM data” fields, equivalent to the fields “UARTl RX synchro” 54 and “UARTl RX datai” for example. However, these two fields do not have a fixed direction, but vary between input or output depending on the commands sent or received by the SIM card.

It is therefore necessary to free two bits in the frame described above in relation to FIG. 4, in order to be able to transport there the signaling and / or control data of the bidirectional port of the SIM card. For this, the two variants mentioned above can be combined, that is to say using four types of preamble in order to delete the “audio synchro” field 51 and the “UARTl RX synchro” field 54.

It should be noted that during the initialization phase of the SIM card, the transaction between the SIM card and the radiocommunication module must be forced to freeze at the maximum communication speed allowed by the method according to the invention (i.e. 57 600 baud maximum in the above example).

Claims

1. Method for transmitting digital data between a master device and a slave device, the transmitted data comprising audio data and signaling and / or control data, the master device generating an audio bit clock and an audio sampling clock , characterized in that the data are transmitted in synchronous frames each comprising a preamble and a useful part, the useful part of each frame comprising at least one audio data field and at least one signaling and / or control data field , the preambles being sent by the master device at the frequency of the audio bit clock and having a predetermined structure, so that the slave device detects the preambles and covers the audio bit clock.

2. Method according to claim 1, characterized in that the useful part of each frame comprises: at least a first audio data field ("audio Tx data"), used for the transmission of audio data from the master device to the device slave ; at least one second audio data field (“audio Rx data”), used for the transmission of audio data from the slave device to the master device.

3. Method according to any one of claims 1 and 2, characterized in that the master device transmits at least a first and a second type of preamble, and in that the second type of preamble is used only for a frame every M frames, with M the ratio between the frequency of the audio bit clock and the frequency of the audio sampling clock, so that the slave device detects the preambles of the second type and covers the audio sampling clock.

4. Method according to any one of claims 1 and 2, characterized in that the useful part of each frame comprises a first signaling and / or control data field (“audio synchro”) which may contain a first or a second information, and in that the first signaling and / or control data field contains the second information for a frame every M frames, with M the ratio between the frequency of the audio bit clock and the frequency of the audio sampling clock, so that the slave device detects the first signaling and / or control data fields containing the second information and overlaps the sampling clock audio.

5. Method according to one of claims 3 and 4, characterized in that the useful part of each frame comprises at least a second field of signaling and / or control data ("GPIO data", "UARTl control data") in which are temporally multiplexed, according to a pattern of M successive frames, data relating to the state of P signaling and / or control signals (“GPIO”, “UARTl control”), with P ≤ M, said at least a second signaling and / or control data field being used, for each row of the pattern of M successive frames, in a predetermined manner either for the transmission of data from the master device to the slave device, or for the transmission of data from the slave device to the master device.

6. Method according to one of claims 1 to 5, characterized in that the useful part of each frame comprises at least a third signaling and / or control data field (“GPS TX”) in which data are transmitted relating to the state of a first serial signaling and / or control port (“GPS serial port”), said at least one third field of signaling and / or control data being used in a predetermined manner either for transmission data from the master device to the slave device, ie for the transmission of data from the slave device to the master device.

7. Method according to any one of claims 1 to 6, characterized in that the master device transmits at least a third and a fourth type of preamble, in that the useful part of each frame comprises at least a fourth data field signaling and / or control ("UARTl TX datai", "UARTl TX data2") in which data relating to the state of a transmission channel of a second serial signaling port and / or control (“serial port UARTl”), said at least one fourth signaling and / or control data field being used for the transmission of data from the master device to the slave device, and in that the fourth type of preamble is used after the master device has detected a start bit on the transmit channel of the second serial port, the fourth type of preamble indicating that the eight consecutive bits carried by the fourth (s) signaling and / or control data field (s) transport a byte of the transmission channel of the second serial port, so that the slave device detects the preambles of the fourth type and generates bytes, each preceded by a start bit, in the format of the second serial port.

8. Method according to any one of claims 1 to 6, characterized in that the useful part of each frame comprises at least a fourth signaling and / or control data field ("UARTl TX datai", "UARTl TX data2 ") In which data relating to the state of a transmission channel of a second serial signaling and / or control port (" serial port UARTl ") are transmitted, said at least one fourth data field of signaling and / or control being used for the transmission of data from the master device to the slave device, and in that the useful part of each frame comprises a fifth field of signaling and / or control data ("UARTl TX synchro ”) May contain third or fourth information, and in that the fifth signaling and / or control data field contains the fourth information if the master device has detected a start bit on the second serial port transmit channel, the fourth information indicating that the eight consecutive bits carried by the fourth or more signaling and / or control data field (s) carry one byte of the second transmit channel serial port, so that the slave device detects the fifth signaling and / or control data fields containing the fourth information, and generates bytes, each preceded by a start bit, in the format of the second serial port.

9. Method according to any one of claims 7 and 8, characterized in that the useful part of each frame comprises at least two fourth fields of signaling and / or control data ("UARTl TX datai", "UARTl TX data2 ”) Distant about half the length of said frame, so that the slave device can process without prior storage the content of each of the fourth signaling and / or control data fields.

10. Method according to any one of claims 7 to 9, characterized in that the size of or all of the fourth (s) field (s) of signaling and / or control data ("UARTl TX datai" , "UARTl TX data2") is such that the bit rate that it carries (s) is sufficient so that neither the master device nor the slave device has to memorize in full each byte of the transmission channel of the second serial port.

11. Method according to any one of claims 1 to 10, characterized in that the master device transmits at least a fifth and a sixth type of preamble, in that the useful part of each frame comprises at least a sixth data field signaling and / or control ("UARTl RX datai", "UARTl RX data2") in which data relating to the state of a reception channel of a second serial signaling and / or control port are transmitted (“Serial port UARTl”), said at least one sixth signaling and / or control data field being used for the transmission of data from the slave device to the master device, and in that the sixth type of preamble is used after the slave device has detected a start bit on the reception channel of the second serial port, the sixth type of preamble indicating that the eight consecutive bits carried by the sixth field (s) of signaling and / or control data transport a byte of the reception channel of the second serial port, so that the master device detects the preambles of the sixth type and generates bytes, each preceded by a start bit, in the format of the second serial port.

12. Method according to any one of claims 1 to 10, characterized in that the useful part of each frame comprises at least a sixth signaling and / or control data field ("UARTl RX datai", "UARTl RX data2 ”) In which data relating to the state of a reception channel of a second serial signaling and or control port (“ serial port UARTl ”) are transmitted, said at least one sixth signaling data field and / or control being used for the transmission of data from the slave device to the master device, and in that the useful part of each frame comprises a seventh signaling and / or control data field (“UARTl RX synchro”) may contain fifth or sixth information, and in that the seventh signaling and / or control data field contains the sixth information if the slave device has detected a start bit on the reception channel of the second serial port, the sixth information indicating that the eight consecutive bits carried via the sixth signaling and / or control data field (s) transport a byte of the reception channel of the second serial port, so that the master device detects the seventh signaling data fields and / or control containing the sixth information, and generates bytes, each preceded by a start bit, in the format of the second serial port.

13. Method according to any one of claims 11 and 12, characterized in that the useful part of each frame comprises at least two sixth fields of signaling and / or control data ("UARTl RX datai", "UARTl RX data2 ”) Distant about half the length of said frame, so that the master device can process the contents of each of the sixth signaling and / or control data fields without prior storage.

14. Method according to any one of claims 11 to 13, characterized in that the size of or all of the sixth (s) field (s) of signaling and / or control data ("UARTl RX datai" , "UARTl RX data2") is such that the bit rate it carries is sufficient so that neither the master nor the slave device has to memorize in full each byte of the reception channel of the second port series.

15. Method according to any one of claims 1 to 14, characterized in that the preamble has two rising or falling edges separated by a predetermined number NI of clock strokes of a reference clock, such as:

NI ≠ N2, with N2 = k.N, k being an integer greater than or equal to one, N being the number of strokes of the reference clock used for each bit of the useful part of each frame;

NI ≠ N3, with N3 the number of strokes of the reference clock separating the last rising edge, or falling edge, inside the useful part of the previous frame and the first rising edge, or falling edge, inside the preamble of the current frame; - NI ≠ N4, with N4 the number of strokes of the reference clock separating the last rising or falling edge inside the preamble of the frame current and the first rising or falling edge inside the useful part of the current grid.

16. Method according to claim 15, characterized in that: NI = 12, N3 = N4 = 18 and N = 8.

17. Method according to any one of claims 1 to 16, characterized in that the frequency of the audio bit clock is 64 kHz, and in that the frequency of the audio sampling clock is 8 kHz.

18. Method according to any one of claims 1 to 17, characterized in that the data are transmitted between the master device and the slave device on a medium conforming to the physical layer of the CAN bus protocol.

19. Application of the method according to any one of claims 1 to 18 to the transmission of digital data between: a master device comprising a radiocommunication module allowing access to a radiocommunication network and - a slave device comprising means for use and / or control of the radiocommunication module.

20. Application according to claim 19, characterized in that the master device is located in a first part of a motor vehicle, preferably a trunk, and in that the slave device is located in a second part of said motor vehicle, preferably a dashboard.

21. Application according to claim 19, characterized in that the master device is located outside an elevator car and in that the slave device is located inside said elevator car.

22. System for transmitting digital data between a master device and a slave device, the transmitted data comprising audio data and signaling and / or control data, the master device generating an audio bit clock and an audio sampling clock , characterized in that the master device comprises: means for generating synchronous frames in which the data are transmitted and each comprising a preamble and a useful part, the part useful of each frame comprising at least one audio data field and at least one signaling and / or control data field; means for transmitting the preambles at the frequency of the audio bit clock and with a predetermined structure; and in that the slave device comprises: means for detecting preambles; means for recovering the audio bit clock.

23. The system as claimed in claim 22, characterized in that the master device and the slave device are connected by a support conforming to the physical layer of the CAN bus protocol and on which the digital data are transmitted.

24. Master device, characterized in that it comprises means for implementing the method, according to any one of claims 1 to 18, for transmitting digital data between said master device and a slave device.

25. Master device according to claim 24, characterized in that it comprises: - means for generating synchronous frames in which the data are transmitted and each comprising a preamble and a useful part, the useful part of each frame comprising at least an audio data field and at least one signaling and / or control data field; means for transmitting the preambles at the frequency of the audio bit clock and with a predetermined structure; so that the slave device detects the preambles and covers the audio bit clock.

26. Slave device, characterized in that it comprises means for implementing the method, according to any one of claims 1 to 18, for transmitting digital data between a master device and said slave device.

27. Slave device according to claim 26, characterized in that it comprises: means for detecting the preambles; means for recovering the audio bit clock.

28. Signal transporting digital data between a master device and a slave device, the transported data comprising audio data and signaling and / or control data, the master device generating an audio bit clock and an audio sampling clock, characterized in that the signal has a structure with synchronous frames each comprising a preamble and a useful part, the useful part of each frame comprising at least one audio data field and at least one signaling and / or control data field , the preambles being sent by the master device at the frequency of the audio bit clock and having a predetermined structure, so that the slave device detects the preambles and covers the audio bit clock.