Title of Invention	ELECTRICAL INSULATING DEVICE FOR BI-DIRECTIONAL CONNECTING LINES (CTL[CO:1] D[0.7]) CONNECTING TWO ELECTRONIC CIRCUIT UNITS (10:20) TO ONE ANOTHER
Abstract	The invention relates to an electrical insulation for bidirectional connecting lines (CTL[0:1], D [0.7] ) connecting two electronic circuit units (10,20) to one another; said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7] ), the device comprises at least one optocoupler providing electrical insulation. Either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTLC0:103, D [0:7] ) and in that a control unit (33) is provided, which generates switching signals (EN, EN), the switching signals (EN,EN) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7] ), or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1]), D [0:7] in a direction opposite to the previous signal flow direction.

Title of Invention

ELECTRICAL INSULATING DEVICE FOR BI-DIRECTIONAL CONNECTING LINES (CTL[CO:1] D[0.7]) CONNECTING TWO ELECTRONIC CIRCUIT UNITS (10:20) TO ONE ANOTHER

Abstract

The invention relates to an electrical insulation for bidirectional connecting lines (CTL[0:1], D [0.7] ) connecting two electronic circuit units (10,20) to one another; said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7] ), the device comprises at least one optocoupler providing electrical insulation. Either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTLC0:103, D [0:7] ) and in that a control unit (33) is provided, which generates switching signals (EN, EN), the switching signals (EN,EN) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7] ), or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1]), D [0:7] in a direction opposite to the previous signal flow direction.

Full Text	The invention relates to an electrical insulation device for.bidirectional connecting lines/bus lines with the use of optocouplers. Prior Art The invention is based on an electrical insulation device for bidirectional connecting lines of the generic type of the independent Claims 1 and 2. If a plurality of independent apparatuses are interconnected via lines, then it is often necessary to provide electrical insulation between the interconnected components. This applies particularly whenever the connected apparatuses are installed e.g. in a manner distributed in a building. This is because in this situation relatively large potential differences between the apparatuses can occur, which are caused e.g. by different potentials on the power supply lines. Such potential differences may occur in the range from a few millivolts up to a number of volts. Potential differences of this type may be present with greater or lesser stability. They may vary e.g. in accordance with the instantaneous total power consumption in the building. However, they may also fail momentarily, with destructive effect, e.g. due to a lightning strike in the building itself or in the vicinity of the building. In the less severe case, the data signals and/or control signals which run via the bus connections are merely corrupted. However, they can lead to the destruction of the connected circuit sections. The problem of undesirable earth loops, caused by the connecting lines, frequently arises. By way of example, induced current can flow through the cable screen of the bus connection and likewise corrupt the transmitted data signals. If the induced potential difference is large enough, persons who happen to be PD99tT054-Sj 2 handling the corresponding bus connection cable could also be injured. Therefore, the requirement for complete electrical isolation of the stations which are connected to one another by lines is necessary. One example of a bus system in which electrical isolation of the components which are connected to one another is required is the IEEE 1394 bus standard, which has recently acquired increasing importance. The exact designation of this bus standard reads as follows: IEEE Std 1394-1995, "IEEE Standard for a high performance serial bus" of 12.12.1995. What is involved is a bus system containing two data line pairs and also two power supply lines earth and Vcc and also a cable screen in the bus connection cable. The two data line pairs allow synchronous serial data transmission. What is probably one of the most outstanding properties of the bus system is that data transmission is possible at very high data rates of 100 megabits per second up to 400 megabits per second. With regard to the realization of electrical isolation of stations which are connected to one another via the bus, two explicit circuit realizations are specified in Appendix J.6 of the abovementioned standard. In both cases, electrical isolation is performed between ' the data link layer module and the physical layer module. A transformer connected up appropriately with resistors and capacitors is used for the electrical isolation in one case, and capacitive decoupling is provided for the electrical isolation in the other case. These solutions have assumed, however, that the data link layer module and the physical layer module are present as separate chips. It has been shown in retrospect that the capacitive isolation of the two modules does not constitute a reliable solution in practice at the high frequencies. Instances of signal corruption and interfering irradiation have occurred. In the case of electrical insulation using a transformer, moreover, PD990054-SJ 3 there is the disadvantage that this solution can no longer be used if the data link layer module and the physical layer module of the bus interface are intended to be integrated on a single chip. Furthermore, it is known to use so-called optocouplers for the electrical isolation of circuit units which are connected to one another. Invention The object of the invention is to specify an electrical insulation device in particular for bidirectional connecting lines which operates reliably even at very high frequencies and can be integrated very ^ - fiasi 1 v on a r.hi n . The object is achieved by means of the features of the independent Claims 1 and 2. In accordance with a first embodiment of the invention, the electrical insulation device for bidirectional connecting lines comprises two separate optocouplers per bidirectional connecting line and a control unit, which generates switching signals in a manner dependent on control signals output by one of the two circuit units, which switching signals, via corresponding switches, activate one of the two optocouplers and deactivate the other optocoupler, and thus allow transmission of signals via the connecting line in one direction. This solution does not require poorly integrable components such as transformers. Moreover, the aforementioned control unit can be constructed in a simple manner and can be readily integrated on a chip. The second solution according to the invention in accordance with Claim 2 manages with just one optocoupler per bidirectional connecting line. This is achieved by modifying the control unit in such a way that, in a manner dependent on the control signals output by one of the two circuit units which are connected to one another, the said control unit changes over the effective direction of the optocoupler with regard to the PD990054-SJ 4 associated connecting line. In this case, it is necessary merely to provide two more switches for the switching operations. The implementation of such switches does not constitute a problem for the chip design. Therefore, this solution provides an electrical insulation device which can be integrated in a particularly simple manner. Further advantageous developments and improvements of the devices mentioned in Claims 1 and 2 are possible by virtue of the measures evinced in the dependent claims. In accordance with Claim 4, the electrical insulation device may very advantageously be provided between a data link layer module and a physical layer module of a bus interface. If the solution is used in the case of an IEEE 1394 bus interface, then it suffices for the respective control unit to evaluate the' control signals on the two control lines CTL [0:1] of the connecting bus between the two modules in order to activate the corresponding optocoupler or to change over the effective direction of the optocoupler. Tristate drivers, in particular, may expediently be used as switches for the changeover between the optocouplers or for changing over the effective direction of the optocoupler, the said tristate drivers being driven correspondingly by the control unit. PD990054-SJ 5 Drawings The exemplary embodiments of the invention are illustrated in the,^ drawings ^and are explained, in more detail in the description below. In the figures: Figure 1 shows the connecting lines between the data link module and the physical layer module in accordance with the IEEE 1394 standard; Figure 2 shows the basic arrangement of the data link layer module, the electrical insulation device and;the physical layer module; Figure 3 shows the structure of the electrical insulation device in accordance with a first exemplary embodiment of the invention; Figure 4 shows a state diagram of the control unit of the electrical insulation device as shown in Figure 3; Figure 5 shows the structure of the electrical insulation device in accordance with a second exemplary embodiment of the invention. Exemplary Embodiments of the Invention The invention is explained using the example of an electrical 'insulation device for an IEEE 1394 bus interface. Figure 1 shows the basic structure of an IEEE 1394 bus interface. The latter comprises the two modules data link layer module 10 and physical layer module 20. These two modules may be integrated on separate chips. It is desirable, however, for these modules to be integrated together on a single chip. The connection between the modules is effected by two bidirectional control lines CTL[0:l], and e.g. eight bidirectional data lines D[0:7], and also a unidirectional control line LREQ proceeding from the data link layer module, and also a control line SCLK for the system clock, proceeding from the physical layer module. For the sake of clarity, it is also mentioned that the connection to a further IEEE 1394 bus interface is effected via external connecting lines which PD990054-SJ 6 are not illustrated and are connected to the physical layer module 20. Accordingly, the data link layer module 10 contains connections which connect the IEEE 1394 bus interface to an application unit. For further details regarding the structure and the method of .ope^ataon of the modules data link layer module and physical layer module, reference is made to the IEEE 1394 standard already mentioned above. In accordance with a proposal in the IEEE 1394 standard, the electrical insulation device 30 is provided between the data link layer module 10 and the physical layer module 20. This is illustrated in Figure 2. The structure of the electrical insulation device 30 is represented for a first exemplary embodiment in Figure 3, in.which an optocoupler unit is designated by the reference numeral 31. This unit contains two separate optocouplers 311, 312. The latter are reverse-connected in parallel, so that the light-emitting element of one optocoupler is connected to that part of the bidirectional connecting line which is connected to the data link layer module 10, and the light-emitting element of the other optocoupler is fed by that part of the connecting line which is connected to the physical layer module. In the example shown, the control line CTL[0] is connected to the optocoupler unit 31. Between the two optocouplers, a respective tristate driver 32 is connected on each side of the optocoupler unit 31. The two tristate drivers 32 illustrated are switched by complementary enable signals EN and EN. This will be discussed in more detail below. The tristate drivers 32 have the following effect. They can be switched either into a high-impedance state or into a low-impedance state in which they allow signals to pass. If we suppose that the tristate driver 32 on the side of the data link layer module 10 is switched in a low-impedance manner, a signal flow is possible via the control line CTL [0] proceeding from the physical layer module 20 via the lower optocoupler 312 to the data link layer module 10. The PD990054-SJ 7 reverse signal flow is simultaneously inhibited, since the tristate driver 32 on the side of the physical layer module 20 is simultaneously switched in a high-impedance manner. In parallel with this, it is also possible, of course, to effect a switch-off of the upper optocoupler at the same time. In the reverse case, that is to say if the left-hand tristate driver 32 is switched in a high-impedance manner and the right-hand tristate driver 32 is switched in a low-impedance manner, a signal flow is possible from the data link layer module 10 to the physical layer module 20 via the control line CTL[0]. The changeover of the tristate drivers 32 is effected with the aid of the control signals EN and EN by the control unit 33. To that end, the control unit 33 evaluates the signal states on the two control lines CTL[0:l]. For complete functioning, the clock signal SCLK or a clock signal modified therefrom and also a reset signal are additionally fed to the control unit 33. The IEEE 1394 standard provides for the physical layer module 20 to have control over the bidirectional connecting lines CTL[0:l] and D[0:7]. The data link layer module 10 is permitted to drive these bidirectional connecting lines only when the physical layer module 20 relinquishes :its control over these lines to the data link layer module 10. A full explanation of when and how the physical layer module 20 relinquishes its control over the bidirectional connecting lines can be found in Appendix J of the IEEE 1394 standard. A s'tate diagram for the control unit 33, which fulfils the specifications of the IEEE 1394 standard, is shown in Figure 4 and is explained in more detail below. Before that explanation, it is also pointed out that the structure shown in Figure 3 with the tristate drivers 32 and the optocoupler arrangement 31 must be present for each of the bidirectional connecting lines between data link layer module 10 and physical layer module 20, that is to say for the control lines CTL[0:l] and the data lines D [ 0:7 ] . For the two unidirectional PD990054-SJ 8 control lines LREQ and SCLK, simple optocouplers must be present in a complete electrical insulation device, which optocouplers, however, only have to act in one direction in accordance with the unidirectionality of these lines. That state diagram of the control unit 33 shows 4 states. After a reset or after the initialization of the bus interface, the control unit 33 is put into the state IDLE. In this state, the control unit outputs the logic states EN=0 and EN=1 as output signals. This is equivalent to the changeover of the left-hand tristate driver 32 of Figure 3 into the low-impedance state and the changeover of the right-hand tristate driver 32 into the high-impedance state. The signal flow via all the bidirectional lines therefore proceeds from the physical layer module 20 to the data link layer module 10. This state is left if the logic level 1 has been detected in a clock cycle on both control lines CTL[0] and CTL[l]. The control unit 33 is then put into the state CHECKO. It then awaits the state of the two control lines in the next clock cycle. If both control lines have the state logic 0, the control unit 33 is put into the state LINK. In all other cases, the control unit 33 returns to the IDLE state. In the LINK state, the combination EN=1 and EN=0 is output as output signal. This is equivalent to the relinquishing of control over the bidirectional connecting lines to the data link layer module 10. Consequently, the left-hand tristate driver 32 of Figure 3 is then put into the high-impedance state and the right-hand tristate driver 32 is switched to the low-impedance state. Thus, the signal flow for all the bidirectional lines then proceeds from the data link layer module 10 to the physical layer module 20. If, in this state, the logic 0 state arises on both control lines CTL[0:l], then the control unit 33 leaves the LINK state and changes over to the CHECK1 state. In this state, a check is made to determine whether the logic state 0 is likewise supplied via both control lines in the subsequent clock cycle. If this is the case, the PD990054-SJ 9 control unit 33 changes back to the IDLE state. Otherwise, it changes over to the LINK state. The alternative embodiment of an electrical isolation device according to the invention will now be explained in more detail with reference to Figure 5. Similar components are designated by the same reference symbols as in Figure 3. The difference from the solution as shown in Figure 3 consists in the fact that, in the optocoupler unit 31, only one optocoupler is provided per bidirectional connecting line. However, the effective direction of the said optocoupler is changed over in a manner dependent on the signals on the control lines CTL[O:1] . This is effected by 4 tristate drivers 32 per connecting line. In this case, the control unit 33 is constructed in exactly the same way as in the example of Figure 3. It functions according to the same state diagram as illustrated in Figure 4. Thus, in the IDLE state, it will output the logic states 0 and 1 via the lines EN and EN. As a result, the first of the two tristate drivers 32 on the left-hand side of Figure 5 is switched in a high-impedance manner and the second tristate driver is accordingly switched in a low-impedance manner. Accordingly, the first of the two tristate drivers on the right-hand side of Figure 5 is likewise switched in a high-impedance manner and the other in a low-impedance manner. The signal flow is then as follows. The signal flows via the data line D[0] proceeding from the physical layer module 20 as transmitter to the second tristate driver 32 on the left-hand side of Figure 5 via the optocoupler to the second tristate driver 32 on the right-hand side of Figure 5 and from there to the data link layer module. In the other state LINK, the logic signals 1 and 0 are output on the lines EN and EN . This changes over the signal flow. As a result, the data link layer module 10 operates as transmitter. The data pass through the first tristate driver 32 on the left-hand side of Figure 5, the optocoupler in the optocoupler unit 31, the first PD990054-SJ 10 tristate driver 32 on the right-hand side of Figure 5 and pass from there to the input of the physical layer module 20. The above-described embodiments of an electrical insulation device can be advantageously used not just for the IEEE 1394 bus standard. They can be employed wherever1 bidirectional connecting lines are intended to be provided with electrical insulation. This problem can also arise in other bus systems. We Claim: 11. 1. Electrical insulation device for bi-directional connecting lines ( CTL[0:1], D [0:7]) connecting two electronic circuit units (10, 20) to one another^ said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7]), the device comprises at least one optocoupler providing electrical insulation, characterized in that, either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTL[0:10], D [0:7], and in that a control unit (33) is provided, which generates switching signals ( EN, EN ), the switching signals ( EN, EN ) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7], or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1], D[0:7] in a direction opposite to the previous signal flow direction. 2. Electrical insulation device as claimed in claim 1, wherein the bi-directional connecting lines ( CTL[0:1], D[0:7] relate either to a data line ( D[0:7]) or to a control line (CTL[0:1]. 3. Electrical insulation device as claimed in claim 1 or 2, wherein the circuit units (10, 20) which are connected to one another via the connecting lines relate to 12. the circuit blocks, data link layer block (10) and physical layer block ( 20) of a connection interface, in particular IEEE 1394 bus interface. 4. Electrical insulation device as claimed in claim 3, wherein the respective control unit (33) evaluates the control signals on the control lines ( CTL[0:1]) of the connecting bus between data link layer block (10) and physical layer block ( 20) in accordance with the IEEE 1394 Standard. 5. Electrical insulation device as claimed in one of claims 1 to 4, wherein at least one tristate driver (32), which is switched into corresponding states by the control unit (33), being used for changing over between the optocouplers or for changing over the effective direction of one optocoupler. The invention relates to an electrical insulation for bidirectional connecting lines (CTL[0:1], D [0.7] ) connecting two electronic circuit units (10,20) to one another; said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7] ), the device comprises at least one optocoupler providing electrical insulation. Either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTLC0:103, D [0:7] ) and in that a control unit (33) is provided, which generates switching signals (EN, EN), the switching signals (EN,EN) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7] ), or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1]), D [0:7] in a direction opposite to the previous signal flow direction.

Full Text

The invention relates to an electrical insulation device for.bidirectional connecting lines/bus lines with the use of optocouplers.
Prior Art
The invention is based on an electrical insulation device for bidirectional connecting lines of the generic type of the independent Claims 1 and 2. If a plurality of independent apparatuses are interconnected via lines, then it is often necessary to provide electrical insulation between the interconnected components. This applies particularly whenever the connected apparatuses are installed e.g. in a manner distributed in a building. This is because in this situation relatively large potential differences between the apparatuses can occur, which are caused e.g. by different potentials on the power supply lines. Such potential differences may occur in the range from a few millivolts up to a number of volts. Potential differences of this type may be present with greater or lesser stability. They may vary e.g. in accordance with the instantaneous total power consumption in the building. However, they may also fail momentarily, with destructive effect, e.g. due to a lightning strike in the building itself or in the vicinity of the building.
In the less severe case, the data signals and/or control signals which run via the bus connections are merely corrupted. However, they can lead to the destruction of the connected circuit sections.
The problem of undesirable earth loops, caused by the connecting lines, frequently arises. By way of example, induced current can flow through the cable screen of the bus connection and likewise corrupt the transmitted data signals. If the induced potential difference is large enough, persons who happen to be

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handling the corresponding bus connection cable could also be injured.
Therefore, the requirement for complete electrical isolation of the stations which are connected to one another by lines is necessary.
One example of a bus system in which electrical isolation of the components which are connected to one another is required is the IEEE 1394 bus standard, which has recently acquired increasing importance. The exact designation of this bus standard reads as follows: IEEE Std 1394-1995, "IEEE Standard for a high performance serial bus" of 12.12.1995.
What is involved is a bus system containing two data line pairs and also two power supply lines earth and Vcc and also a cable screen in the bus connection cable. The two data line pairs allow synchronous serial data transmission. What is probably one of the most outstanding properties of the bus system is that data transmission is possible at very high data rates of 100 megabits per second up to 400 megabits per second.
With regard to the realization of electrical isolation of stations which are connected to one another via the bus, two explicit circuit realizations are specified in Appendix J.6 of the abovementioned standard. In both cases, electrical isolation is performed between ' the data link layer module and the physical layer module. A transformer connected up appropriately with resistors and capacitors is used for the electrical isolation in one case, and capacitive decoupling is provided for the electrical isolation in the other case. These solutions have assumed, however, that the data link layer module and the physical layer module are present as separate chips. It has been shown in retrospect that the capacitive isolation of the two modules does not constitute a reliable solution in practice at the high frequencies. Instances of signal corruption and interfering irradiation have occurred. In the case of electrical insulation using a transformer, moreover,

PD990054-SJ
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there is the disadvantage that this solution can no longer be used if the data link layer module and the physical layer module of the bus interface are intended to be integrated on a single chip.
Furthermore, it is known to use so-called optocouplers for the electrical isolation of circuit units which are connected to one another.
Invention
The object of the invention is to specify an
electrical insulation device in particular for
bidirectional connecting lines which operates reliably
even at very high frequencies and can be integrated very
^ -
fiasi 1 v on a r.hi n .
The object is achieved by means of the features of the independent Claims 1 and 2. In accordance with a first embodiment of the invention, the electrical insulation device for bidirectional connecting lines comprises two separate optocouplers per bidirectional connecting line and a control unit, which generates switching signals in a manner dependent on control signals output by one of the two circuit units, which switching signals, via corresponding switches, activate one of the two optocouplers and deactivate the other optocoupler, and thus allow transmission of signals via the connecting line in one direction. This solution does not require poorly integrable components such as transformers. Moreover, the aforementioned control unit can be constructed in a simple manner and can be readily integrated on a chip.
The second solution according to the invention in accordance with Claim 2 manages with just one optocoupler per bidirectional connecting line. This is achieved by modifying the control unit in such a way that, in a manner dependent on the control signals output by one of the two circuit units which are connected to one another, the said control unit changes over the effective direction of the optocoupler with regard to the

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associated connecting line. In this case, it is necessary merely to provide two more switches for the switching operations. The implementation of such switches does not constitute a problem for the chip design. Therefore, this solution provides an electrical insulation device which can be integrated in a particularly simple manner.
Further advantageous developments and improvements of the devices mentioned in Claims 1 and 2 are possible by virtue of the measures evinced in the dependent claims. In accordance with Claim 4, the electrical insulation device may very advantageously be provided between a data link layer module and a physical layer module of a bus interface. If the solution is used in the case of an IEEE 1394 bus interface, then it suffices for the respective control unit to evaluate the' control signals on the two control lines CTL [0:1] of the connecting bus between the two modules in order to activate the corresponding optocoupler or to change over the effective direction of the optocoupler.
Tristate drivers, in particular, may expediently be used as switches for the changeover between the optocouplers or for changing over the effective direction of the optocoupler, the said tristate drivers being driven correspondingly by the control unit.

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Drawings
The exemplary embodiments of the invention are illustrated in the,^ drawings ^and are explained, in more detail in the description below. In the figures:

Figure 1 shows the connecting lines between the data link module and the physical layer module in accordance with the IEEE 1394 standard;
Figure 2 shows the basic arrangement of the data link layer module, the electrical insulation device and;the physical layer module;
Figure 3 shows the structure of the electrical insulation device in accordance with a first exemplary embodiment of the invention;
Figure 4 shows a state diagram of the control unit of the electrical insulation device as shown in Figure 3;
Figure 5 shows the structure of the electrical insulation device in accordance with a second exemplary embodiment of the invention.

Exemplary Embodiments of the Invention
The invention is explained using the example of an electrical 'insulation device for an IEEE 1394 bus interface. Figure 1 shows the basic structure of an IEEE 1394 bus interface. The latter comprises the two modules data link layer module 10 and physical layer module 20. These two modules may be integrated on separate chips. It is desirable, however, for these modules to be integrated
together on a single chip. The connection between the modules is effected by two bidirectional control lines CTL[0:l], and e.g. eight bidirectional data lines D[0:7], and also a unidirectional control line LREQ proceeding from the data link layer module, and also a control line SCLK for the system clock, proceeding from the physical layer module. For the sake of clarity, it is also mentioned that the connection to a further IEEE 1394 bus interface is effected via external connecting lines which

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are not illustrated and are connected to the physical layer module 20. Accordingly, the data link layer module 10 contains connections which connect the IEEE 1394 bus
interface to an application unit. For further details regarding the structure and the method of .ope^ataon of the modules data link layer module and physical layer
module, reference is made to the IEEE 1394 standard already mentioned above.
In accordance with a proposal in the IEEE 1394 standard, the electrical insulation device 30 is provided between the data link layer module 10 and the physical layer module 20. This is illustrated in Figure 2.
The structure of the electrical insulation device 30 is represented for a first exemplary embodiment in Figure 3, in.which an optocoupler unit is designated by the reference numeral 31. This unit contains two separate optocouplers 311, 312. The latter are reverse-connected in parallel, so that the light-emitting element of one optocoupler is connected to that part of the bidirectional connecting line which is connected to the data link layer module 10, and the light-emitting element of the other optocoupler is fed by that part of the connecting line which is connected to the physical layer module. In the example shown, the control line CTL[0] is connected to the optocoupler unit 31. Between the two optocouplers, a respective tristate driver 32 is connected on each side of the optocoupler unit 31. The two tristate drivers 32 illustrated are switched by complementary enable signals EN and EN. This will be discussed in more detail below. The tristate drivers 32 have the following effect. They can be switched either into a high-impedance state or into a low-impedance state in which they allow signals to pass. If we suppose that the tristate driver 32 on the side of the data link layer module 10 is switched in a low-impedance manner, a signal flow is possible via the control line CTL [0] proceeding from the physical layer module 20 via the lower optocoupler 312 to the data link layer module 10. The

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reverse signal flow is simultaneously inhibited, since the tristate driver 32 on the side of the physical layer module 20 is simultaneously switched in a high-impedance manner. In parallel with this, it is also possible, of course, to effect a switch-off of the upper optocoupler at the same time. In the reverse case, that is to say if the left-hand tristate driver 32 is switched in a high-impedance manner and the right-hand tristate driver 32 is switched in a low-impedance manner, a signal flow is possible from the data link layer module 10 to the physical layer module 20 via the control line CTL[0]. The changeover of the tristate drivers 32 is effected with the aid of the control signals EN and EN by the control unit 33. To that end, the control unit 33 evaluates the signal states on the two control lines CTL[0:l]. For complete functioning, the clock signal SCLK or a clock signal modified therefrom and also a reset signal are additionally fed to the control unit 33.
The IEEE 1394 standard provides for the physical layer module 20 to have control over the bidirectional connecting lines CTL[0:l] and D[0:7]. The data link layer module 10 is permitted to drive these bidirectional connecting lines only when the physical layer module 20 relinquishes :its control over these lines to the data link layer module 10. A full explanation of when and how
the physical layer module 20 relinquishes its control over the bidirectional connecting lines can be found in Appendix J of the IEEE 1394 standard. A s'tate diagram for
the control unit 33, which fulfils the specifications of the IEEE 1394 standard, is shown in Figure 4 and is explained in more detail below.
Before that explanation, it is also pointed out that the structure shown in Figure 3 with the tristate drivers 32 and the optocoupler arrangement 31 must be present for each of the bidirectional connecting lines between data link layer module 10 and physical layer module 20, that is to say for the control lines CTL[0:l] and the data lines D [ 0:7 ] . For the two unidirectional

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control lines LREQ and SCLK, simple optocouplers must be present in a complete electrical insulation device, which optocouplers, however, only have to act in one direction in accordance with the unidirectionality of these lines.
That state diagram of the control unit 33 shows 4 states. After a reset or after the initialization of the bus interface, the control unit 33 is put into the state IDLE. In this state, the control unit outputs the logic states EN=0 and EN=1 as output signals. This is equivalent to the changeover of the left-hand tristate driver 32 of Figure 3 into the low-impedance state and the changeover of the right-hand tristate driver 32 into the high-impedance state. The signal flow via all the bidirectional lines therefore proceeds from the physical layer module 20 to the data link layer module 10. This state is left if the logic level 1 has been detected in a clock cycle on both control lines CTL[0] and CTL[l]. The control unit 33 is then put into the state CHECKO. It then awaits the state of the two control lines in the next clock cycle. If both control lines have the state logic 0, the control unit 33 is put into the state LINK. In all other cases, the control unit 33 returns to the IDLE state. In the LINK state, the combination EN=1 and
EN=0 is output as output signal. This is equivalent to the relinquishing of control over the bidirectional connecting lines to the data link layer module 10. Consequently, the left-hand tristate driver 32 of Figure 3 is then put into the high-impedance state and the right-hand tristate driver 32 is switched to the low-impedance state. Thus, the signal flow for all the bidirectional lines then proceeds from the data link layer module 10 to the physical layer module 20. If, in this state, the logic 0 state arises on both control lines CTL[0:l], then the control unit 33 leaves the LINK state and changes over to the CHECK1 state. In this state, a check is made to determine whether the logic state 0 is likewise supplied via both control lines in the subsequent clock cycle. If this is the case, the

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9
control unit 33 changes back to the IDLE state. Otherwise, it changes over to the LINK state.
The alternative embodiment of an electrical isolation device according to the invention will now be explained in more detail with reference to Figure 5. Similar components are designated by the same reference symbols as in Figure 3. The difference from the solution as shown in Figure 3 consists in the fact that, in the optocoupler unit 31, only one optocoupler is provided per bidirectional connecting line. However, the effective direction of the said optocoupler is changed over in a manner dependent on the signals on the control lines CTL[O:1] . This is effected by 4 tristate drivers 32 per connecting line. In this case, the control unit 33 is constructed in exactly the same way as in the example of Figure 3. It functions according to the same state diagram as illustrated in Figure 4. Thus, in the IDLE state, it will output the logic states 0 and 1 via the lines EN and EN. As a result, the first of the two tristate drivers 32 on the left-hand side of Figure 5 is switched in a high-impedance manner and the second tristate driver is accordingly switched in a low-impedance manner. Accordingly, the first of the two tristate drivers on the right-hand side of Figure 5 is likewise switched in a high-impedance manner and the other in a low-impedance manner. The signal flow is then as follows. The signal flows via the data line D[0] proceeding from the physical layer module 20 as transmitter to the second tristate driver 32 on the left-hand side of Figure 5 via the optocoupler to the second tristate driver 32 on the right-hand side of Figure 5 and from there to the data link layer module. In the other state LINK, the logic signals 1 and 0 are output on the lines EN and EN . This changes over the signal flow. As a result, the data link layer module 10 operates as transmitter. The data pass through the first tristate driver 32 on the left-hand side of Figure 5, the optocoupler in the optocoupler unit 31, the first

PD990054-SJ
10

tristate driver 32 on the right-hand side of Figure 5 and pass from there to the input of the physical layer module 20.
The above-described embodiments of an electrical insulation device can be advantageously used not just for the IEEE 1394 bus standard. They can be employed wherever1 bidirectional connecting lines are intended to be provided with electrical insulation. This problem can also arise in other bus systems.

We Claim: 11.
1. Electrical insulation device for bi-directional connecting lines ( CTL[0:1], D [0:7]) connecting two electronic circuit units (10, 20) to one another^ said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7]), the device comprises at least one optocoupler providing electrical insulation, characterized in that, either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTL[0:10], D [0:7], and in that a control unit (33) is provided, which
generates switching signals ( EN, EN ), the switching signals ( EN, EN ) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7], or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1], D[0:7] in a direction opposite to the previous signal flow direction.
2. Electrical insulation device as claimed in claim 1, wherein the bi-directional
connecting lines ( CTL[0:1], D[0:7] relate either to a data line ( D[0:7]) or to a
control line (CTL[0:1].
3. Electrical insulation device as claimed in claim 1 or 2, wherein the circuit units
(10, 20) which are connected to one another via the connecting lines relate to

12.
the circuit blocks, data link layer block (10) and physical layer block ( 20) of a connection interface, in particular IEEE 1394 bus interface.
4. Electrical insulation device as claimed in claim 3, wherein the respective
control unit (33) evaluates the control signals on the control lines
( CTL[0:1]) of the connecting bus between data link layer block (10) and
physical layer block ( 20) in accordance with the IEEE 1394 Standard.
5. Electrical insulation device as claimed in one of claims 1 to 4, wherein at
least one tristate driver (32), which is switched into corresponding states
by the control unit (33), being used for changing over between the
optocouplers or for changing over the effective direction of one
optocoupler.
The invention relates to an electrical insulation for bidirectional connecting lines (CTL[0:1], D [0.7] ) connecting two electronic circuit units (10,20) to one another; said electrical insulation unit (30) being disposed anywhere along the connecting lines ( CTL[0:1], D [0:7] ), the device comprises at least one optocoupler providing electrical insulation. Either one single optocoupler or two separate optocouplers (311, 312) are provided for the bi-directional connecting line ( CTLC0:103, D [0:7] ) and in that a control unit (33) is provided, which generates switching signals (EN, EN), the switching signals (EN,EN) either change over the effective direction of the single optocoupler with regard to the associated connecting line ( CTL[0:1], D [0:7] ), or activate one of the two optocouplers (311, 312) and deactivate the other optocoupler, for transmission of signals via the associated connecting line ( CTL[0:1]), D [0:7] in a direction opposite to the previous signal flow direction.

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Patent Number

202480

Indian Patent Application Number

IN/PCT/2002/00068/KOL

PG Journal Number

08/2007

Publication Date

23-Feb-2007

Grant Date

23-Feb-2007

Date of Filing

15-Jan-2002

Name of Patentee

THOMSON LICENSING S.A.

Applicant Address

46 QUAI ALPHONSE LE GALLO 92648 BOULOGNE CEDEX

Inventors:

#	Inventor's Name	Inventor's Address
1	GAEDKE KLAUS	SCHAUMANWEG 22, D-30659 HANNOVER
2	SCHUTZE HERBERT	RINGWEG 2,D-29227 CELLE

PCT International Classification Number

H 04 B 10/00

PCT International Application Number

PCT/EP00/06476

PCT International Filing date

2000-07-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19933135.9	1999-07-19	Germany