DE29817002U1 - Coupling device for connecting at least two segments in a network - Google Patents

Description

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Description

Coupling device for connecting at least two segments in a network
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The invention relates to a coupling device for connecting at least two segments in a network according to the preamble of claim 1.

Networks in which several participants are connected to one another for data transmission are already well known. As a network with only one bus is limited by physical conditions and logical specifications in terms of the number of participants and bus length, the network is divided into several segments that are connected to one another via coupling devices, so-called repeaters. A coupling device is connected to the bus segments on both sides with a transceiver each and is essentially used for bidirectional signal regeneration between the two segments. In particular, coupling devices to which more than two segments can be connected and which operate at high transmission speeds have a high power consumption.

The invention is based on the object of creating a coupling device for connecting at least two segments in a network, the power consumption of which can be adapted to the conditions of the respective application.

To solve this problem, the coupling device of the type mentioned at the outset has the features specified in the characterizing part of claim 1. Advantageous further developments are described in the subclaims.

The invention has the advantage that, depending on the requirements of the respective application, only the amount of operating energy that is actually needed needs to be provided. With a modular design of the coupling device,

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Each segment that can be connected to the coupling device has one channel. A coupling device to which more than two segments can be connected therefore has more than two channels for connecting one segment at a time. Since not all channels of a coupling device are used in every application, a coupling device in which unused channels can be switched off independently of the other channels leads to a reduction in the average power consumption required. Depending on the application, the power supply of the coupling device can be designed to be weaker and, since less heat has to be dissipated, simpler measures for heat dissipation are sufficient and the device is subject to fewer restrictions in terms of its area of application. Overall, the costs associated with a coupling device are therefore reduced.

Advantageously, practically all active parts of a transmission path are switched off without mutual influence of the channels if the channels each contain a complete retimer, which is required to compensate for distortions of a received telegram.

A comparatively complex circuit is required to adapt the signals transmitted on a segment to the signal level of the logic circuit. The cost of coupling devices can therefore be reduced by only fitting the adaptation circuit in the coupling device or, in the case of a modular coupling device, only plugging in the corresponding adaptation module when a segment is actually to be connected to the channel in the respective application. Automatic switching off of unused channels can therefore be achieved in a particularly simple and reliable manner if means are available to generate a signal with which the respective channel is switched off in the absence of a circuit for adapting signals received on a segment to the logic circuit of a switchable channel.

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The invention, its embodiments and advantages are explained in more detail below with reference to the drawings in which embodiments of the invention are shown.

Show it:

Figure 1 a network with electrical signal transmission on three segments,

Figure 2 shows a section of a network with partial electrical and optical signal transmission, Figure 3 shows a telegram structure with an attached CRC check mark,

Figure 4 is a block diagram of a coupling device, Figure 5 is a block diagram of a channel of a coupling device, Figure 6 is a flow chart of a segment decoupling, Figure 7 is a flow chart of a segment coupling with transmission of special telegrams and

Figure 8 shows a network with the structure of an optical double ring.

The network according to Figure 1 is divided into three segments 1, 2 and 3. Participants 4 and 5 are connected to segment 1, and participants 7 and 8 are connected to segment 3. Segments 1 and 2 are connected to one another by a repeater 9 as a first coupling device, and segments 2 and 3 are connected to one another by a repeater 10 as a second coupling device. Data transmission is carried out on segments 1 and 3 according to the PROFIBUS DP protocol. Telegrams that are to be transmitted from segment 1 to segment 3 are provided with a CRC check character in the first coupling device 9, which is read as control information in the second coupling device 10 to check that the telegram has been transmitted correctly via segment 2 and is compared with a CRC check character generated from the received telegram. The forwarding of the telegram to segment 3, which operates according to the PROFIBUS DP protocol, is carried out by the second coupling device without the control information used in segment 2. For the sake of clarity, Figure 1 shows a network with

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only three segments. In practice, however, networks with a considerably larger number of segments often occur, so that the possibility of localizing the fault down to the faulty segment represents a considerable advantage. In coupling devices 9 and 10, only two channels are required for segments with electrical signal transmission, so that further channels of the coupling devices can be switched off.

The network in Figure 2 contains segments 11, 12 and 13, on which data is transmitted using electrical signals, as well as segments 14, 15, 16 and 17 with optical transmission. Only a section of the network is shown. Segments 14 and 17 can contain additional coupling devices or participants, which are not shown for the sake of clarity. Participants 18, 19 and 20 are connected to coupling devices 21, 22 and 23 via segments 11, 12 and 13 respectively. Segments 14, 15, 16 and 17 with optical signal transmission have an optical fiber for each transmission direction. For segment 14, these are the optical fibers 141 and 142, for segment 15, the optical fibers 151 and 152, for segment 16, the optical fibers 161 and 162, and for segment 17, the optical fibers 171 and 172. In this embodiment, segments 11, 12, and 13 are constructed according to the RS485 specification, and data is transmitted according to the PROFIBUS DP protocol. To ensure data transmission, only one parity bit is used on segments 11, 12, and 13. Telegrams are transmitted on segments 14, 15, 16, and 17, each of which is supplemented by control information consisting of a 5-bit CRC check character.

Figure 3 shows the structure of a telegram with an attached CRC check character, as can be used in the networks according to Figures 2 and 3. The check character is added to the telegram to detect dynamic errors, e.g. a loose connection on an optical connector, a cold solder joint or

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excessive attenuation of an optical fiber and to obtain a clear localization of the fault location. This measure checks the transmission of a telegram from one coupling device to another, which represents the next receiver of the telegram. In the embodiment shown in Figure 2, a CRC check character is only generated for segments 14, 15, 16 and 17 with optical signal transmission and checked in the next receiver. If a received CRC check character does not match a CRC check character generated in a coupling device, an error counter is increased by one and if they match, it is decreased by one. If the error counter has reached a predeterminable limit, preferably limit 4, the forwarding of telegrams from the faulty segment to neighboring segments is blocked. On segments 11, 12 and 13 with electrical signal transmission according to the RS485 specification, however, no CRC check character is appended to the telegrams. This means that no deviation from the PROFIBUS DP protocol is required on these segments.

Figure 3 shows only the last three bits, two data bits 31 and 32 and a stop bit 33, of a telegram that corresponds to the PROFIBUS DP protocol. Another stop bit 34 is appended to the stop bit 33, followed by five bits 35 ... 39 of a CRC check character. Above the individual bits, arrows pointing downwards indicate the sampling times at which the signal value is sampled in the receiver. After the last bit 39, an idle state prevails for the duration of the following transmission pause, corresponding to the level 40 shown.

In the case of undisturbed telegrams, the end of the telegram can be determined by a TLU (telegram length unit). In the case of disturbed telegrams, this can possibly be ruled out by the disturbance in the case of a telegram according to the PROFIBUS DP protocol. So that the attached CRC check character is always

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can be evaluated and not misinterpreted as part of the faulty telegram, the end of the telegram must be reliably recognized even in the event of faults. In the example shown, an additional stop bit is inserted between the end of the telegram according to the PROFIBUS DP protocol and the start of the CRC check character. Using the two stop bits 33 and 34 that are thus present, the end of any telegram, including a faulty one, can be recognized in the receiver. The end of the telegram is recognized by the fact that no new start bit is detected after the last character, but rather another stop bit follows.

The CRC check character is always appended synchronously to the Telegram characters. Therefore, a character that has been started is extended to eleven bit times even in the event of interference, thus replicating the eleven-bit character grid of a telegram.

A response telegram can appear on the same segment just eleven bit times after the end of an undisturbed telegram. To ensure that the receiver of a coupling device is not triggered by the CRC check character to receive an eleven-bit character, a reception lock is implemented that prevents a restart of an RXD machine after each telegram end for the duration of the CRC check character.

Figure 4 shows the rough structure of the coupling devices 21, 22 and 23 in Figure 2. A channel is provided for each segment that can be connected to the coupling device. The two channels 41 and 42 are designed for optical signal transmission, the channels 43 and 44 for electrical signal transmission on the respective segment. In the embodiment according to Figure 2, for example, the coupling device 22 is connected in such a way that the signals of the optical waveguide 152 of the segment 15 are transmitted via transceivers (not shown) with lines 45 to channel 41, the signals of the optical waveguide 161 of the segment 16 are transmitted via transceivers (not shown) with lines 46 to channel 42 and the electrical

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Lines of segment 12 are routed to channel 43 via transceivers (not shown) with lines 47. The channel is not used and can be switched off separately from the other channels 41, 42 and 43 to reduce energy consumption. In this example, no segment is connected to lines 48 of channel 44. A path control 49 and a switching matrix 50 ensure that a received telegram is distributed to the connected segments. They activate only one of the channels 41 ... 44 at any one time, which remains selected until the end of the telegram. This is also the case if signals arrive on several channels at the same time. For channels 43 and 44, which are designed for electrical signal transmission, a received signal is forwarded on all segments except the segment that is connected to the currently active receiving channel. For channels 41 and 42 for optical signal transmission, a parameter setting can be used to determine whether a received signal should also be sent back on the segment of the currently active receiving channel or not. Sending the received telegram back on the segment of the currently active receiving channel corresponds to the formation of an echo. As long as the data rate of the telegram has not yet been recognized, the path control 49 prevents the forwarding of received signals to the connected segments. For example, in the coupling device 22 in Figure 2, the optical fiber 151 of segment 15, the optical fiber 162 of segment 16 and the electrical lines of segment 12 (see Figure 2) are connected to lines 52, 53 and 54 via transceivers not shown in Figure 4. The signals that are carried on lines 45 ... 48 are usually designated RXD. Lines 52 ... 55 each physically consist of at least two electrical lines, which are intended for a TXD or RTS signal. For echo monitoring in channels 41 and 42, lines 58 and 59 are routed back from the output of the switching matrix 50 to channels 41 and 42.

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The signals on lines 58 and 59 are evaluated in channels 41 and 42 respectively and then, if necessary, passed on to lines 52 and 53 respectively.

The following will explain the functioning of the path control 49 and the switching matrix using the example of a telegram received on segment 12 with electrical signal transmission. The path control 49 recognizes that a telegram is being received from segment 12 by an RTS signal on a line 60 supplied by channel 43, which is generated on the basis of the received signal on line 47 of channel 43. The switching matrix 50 is then set by the path control 49 in such a way that the received telegram is routed to lines 58 and 59. Since no echo formation is set for segment 12 with electrical signal transmission, the telegram is not forwarded to lines 54. A character for identifying the telegram is stored in channels 41 and 42 and the telegram is output on lines 52 and 53 to the segments 15 and 16 connected to it. If the echo of the telegram output on lines 52 generated by the neighboring coupling device 21 is received by channel 41 via lines 45, it can be identified as an echo of this telegram using the stored character for identifying the telegram and is no longer output on lines 56 and 57 by channel 41. In an analogous manner, the echo generated by the neighboring coupling device 23 is also removed from the network.

The pause between a sent telegram and the arrival of a response telegram can be determined by means of a slot time determination 51.

Figure 5 shows a block diagram of channels 41 and 42 from Figure 4. A line 61 feeds a received signal from a connected segment to a so-called RXD machine 62 and a CRC check 63. Using the example of channel 41 in Figure 4

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the line 61 corresponds to one of the lines 45 in Figure 1. The signal regenerated with the RXD machine 62 is fed via a switch 64 and a first-in/first-out (FIFO) memory 65 to a so-called TXD machine 66, which generates an RTS and a TXD signal on lines 67 and an RTS and TXD signal on lines 68. The lines 67 and 68 are connected to the switching matrix 50 as lines 56 and 57 respectively in the block diagram according to Figure 1, using channel 41 as an example. A telegram is output on the lines 67, which has been supplemented by a CRC check character by a CRC generator 69. The telegram is forwarded on lines 68 without a CRC check character, so that the received telegram is output unchanged and is compatible with a transmission protocol of the participants connected to the respective segment. In this exemplary embodiment, lines 68 are used to forward the received telegram to segments with electrical signal transmission. For echo monitoring, i.e. for monitoring the forwarding of a received telegram to the segment of the currently active receiving channel, lines 70 are provided, which, for example, in the channel in Figure 4 are connected to lines 58 to which the switching matrix 50 forwards the received telegram. The output of an AND gate 76 is connected to lines 52 for transmitting the TXD signal using the example of channel 41 in Figure 4. An RTS signal is forwarded directly from a switch 73 to lines 52 via a line 83. A segmentation logic 71 controls the blocking of the forwarding of faulty telegrams to the connected segments and supplies a blocking signal on a line 72 to the switch 73 and the switch 64.

Further functional blocks in Figure 5 are a device for the telegram start test, a delay element 75, a device 77 for determining the telegram length (TLU), a device 8 6 for the activity check and a device 78 for

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Ring monitoring, the functions of which will be explained in more detail later.

Channels 43 and 44 are basically constructed in a similar way to channels 41 and 42. However, the CRC check 63, the switch 73 and parts of the segmentation logic 71 are omitted, since a CRC check character and an exchange of special telegrams on the segments with electrical signal transmission according to the PROFIBUS DP protocol do not occur.

In the following, the basic functionality of a coupling device is first described using the example of the coupling device 22 in Figure. A telegram received, for example, on segment 15 with optical signal transmission is first directed to the RXD machine 62. RXD machine 62, FIFO memory 65 and TXD machine 66 together have the function of a retimer so that distortions of the received telegram do not propagate in the network. In the receive branch of a channel in which a CRC check character is expected as control information, the received telegram is also directed to the CRC check 63 (Figure 5), in which a CRC check character is formed for the received telegram and compared with the received CRC check character. The device 77 for determining the telegram length evaluates the start delimiter of the received telegram and determines the telegram length. It supplies the CRC check 63 and the RXD machine 62 with a signal on lines 84 and 85, respectively, which indicates the end of the telegram. The CRC check 63 thus recognizes that only a stop bit 34 (Figure 3) and the CRC check character follow, and reads the CRC check character attached to the received telegram, which it needs to compare with the self-generated CRC check character. After the comparison has been carried out, the received CRC check character is discarded. Depending on the result of the comparison, an error signal on a line 79 or a good message on a line 80 is output from the CRC check 63 to the segmentation logic 71. If the switches 64 and 73 are closed, the CRC check 63 sends the CRC check character to the segmentation logic 71.

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are closed and when the received telegram is looped through the switching matrix 50 (Figure 4) with lines 58 to the lines 70 (Figure 5), channel 41 sends the received telegram back with a newly generated CRC check character in the CRC generator 69 as control information via lines 52 on the optical fiber 151 of segment 15, which is intended for data transmission in the opposite direction. The CRC check character is also checked in the activated receive channel of the coupling device 21, which receives the echo telegram, in order to detect interference on the optical fiber 151 in the opposite transmission direction. In the receive channel of the coupling device 21, the switch 64 is open so that the received echo telegram does not interfere with the transmitting process taking place at the same time. If the transmission on segment 15 was undisturbed, the new CRC check character matches the one that was discarded, otherwise it does not. Depending on the setting of the switching matrix 50 by the path control 49, in which transmission directions can be preset, the telegram is also sent to the other outputs of the coupling device, in accordance with the respective protocol of the connected segment, with or without an additional CRC check character. In the embodiment shown in Figure 2, a telegram supplemented with the CRC check character is sent to segment 16 and a telegram without an additional CRC check character is sent to segment 12.

Using switches 64 and 73 in the channels of a coupling device, it is also possible to decouple a faulty segment from the network as an error handling measure so that faults cannot affect the entire network. The fault can thus be advantageously limited to the faulty segment of the network.

On the segments 14 ... 17 with optical signal transmission shown in Figure 2, the transmission and reception paths are each separate. If a segment is disconnected, i.e. if the transmission of

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Telegrams from a faulty segment are transmitted via a coupling device to other segments connected to the coupling device, both transmission directions are advantageously blocked. Thus, for example, in the event of a fault in segment 15, after the segment has been disconnected, neither telegrams from segment 15 are transmitted to segments 12 or 16, nor telegrams from segments 12 or 16 to segment 15. This is particularly advantageous if, in a series of segments connected in series, a so-called optical line, the last of the segments with optical signal transmission is faulty. To explain this advantage, the embodiment according to Figure 2 should be modified in such a way that segment 17 is missing and thus segment 16 is the last segment of the optical line. If a fault occurs in the network structure thus obtained on the optical fiber 162 of segment 16, the forwarding of telegrams received on segment 16 to segment 13 is blocked. An active participant 20 therefore no longer receives telegrams on segment 13, on which data transmission is carried out according to the PROFIBUS DP protocol. In multi-master operation according to the PROFIBUS DP protocol, a master that no longer detects any activity on the network begins to send a token to itself and to query for other participants on the network. This is referred to as continuous token sending. If, despite blocking the transmission direction from segment 16 to segment 13, the forwarding of telegrams in the opposite direction, i.e. from segment 13 to segment 16, were to remain enabled, the token and query telegrams of participant 20 as master would be fed into the entire network. In addition, these telegrams would be asynchronous to the telegrams of the rest of the network and would destroy them, so that in extreme cases data transmission on the undisturbed part of the network would be impossible. To avoid this, it is best to block both transmission directions simultaneously when a segment with optical signal transmission is disconnected. Both transmission directions

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are only enabled again when the bidirectional functionality of the segment has been established through the exchange of special telegrams via the disconnected segment.
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On segments 11, 12 and 13 with electrical signal transmission, the two transmission directions cannot be operated independently of one another, as only a single transmission medium with the ability to transmit bidirectionally is used. In practice, it is therefore extremely rare for transmission to be disrupted in one direction and not in the other. Both transmission directions are therefore not blocked simultaneously on segments 11, 12 and 13. For example, despite the forwarding of telegrams received on segment 12 with electrical signal transmission being blocked, telegrams can still be sent to the disrupted segment 12 by the coupling device 22 without having to worry about the network being blocked. This has the advantage that, for example, For example, a passive participant 19 that is connected to the network via a faulty segment 12 with electrical signal transmission and only sends its telegrams as response telegrams to previous call telegrams can still listen to call telegrams. If both transmission directions of segment 12 are blocked simultaneously by coupling device 22, passive participant 19 would no longer receive call telegrams and consequently would no longer send response telegrams. It would no longer be accessible on the network. Due to the disconnection of segment 12, the forwarding of telegrams received on segment 12 to the network is blocked. However, call telegrams on the network reach passive participant 19 and its response telegrams can be advantageously evaluated by coupling device 22 to assess the transmission quality on segment 12. The exchange of special telegrams to determine the elimination of a fault can therefore be dispensed with, and segment 12 is already

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reconnected when undisturbed telegrams are received on segment 12 with electrical signal transmission. This procedure is also advantageously used for the other segments 11 and 13 with electrical signal transmission.

A sporadic fault, for example on segment 12, therefore leads to a disconnection of the segment for only a few telegrams and does not separate a passive participant from the network for a longer period of time. This allows a better adaptation of the segmentation time to the type of fault: In the case of a sporadic fault, the segment is reconnected after a short time, while in the case of a massive fault, for example a cable break, the disconnection of the segment remains permanent.

The FIFO memory 65 in Figure 5 is used to compensate for bit time fluctuations, which can arise, for example, as a result of quartz inaccuracies during data transmission. If four bits are written into the FIFO memory 65, it begins to output the first bits. The memory depth of the FIFO memory 65 is nine bits.

The TXD machine 66 reads the bits stored in the FIFO memory 65 at a fixed interval of one bit time. The RTS signal (request to send) controls the data flow direction of the transceiver of the respective channel and becomes active four bit times before the first start bit of the telegram. The RTS signal is switched inactive again by the TXD machine 66 at the end of the last stop bit.

The ring monitoring 7 8 consists of a number of monitoring mechanisms that can detect circulating telegrams, telegram fragments or interference in a connection of coupling devices to an optical single-fiber ring or to an optical double ring and can eliminate them by interrupting the ring. An optical single-fiber ring is

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For example, the network structure in Figure 2 is referred to, which exists due to the echo formation ζ. B. on the segment 16 with the connected coupling devices 22 and 23. An optical double ring is obtained by connecting the optical fibers 141 and 142 of segment 14 with the optical fibers 171 and 172 of segment 17, respectively.

A monitoring mechanism implemented in the ring monitoring 78 is a low-bit monitoring that outputs an error signal if the data signal is at the active level, here the low level, for 13 bit times in a row. With valid telegram characters, such a character can never occur in the undisturbed case because of the stop bit with a high level. Causes of such a disturbance can be, for example, external light coupling or a defective coupling device.

Another monitoring mechanism is a transmission time monitor, which outputs an error signal if a telegram contains more than 262 characters. The PROFIBUS DP protocol limits a telegram to a maximum of 255 characters, so that a telegram with more than 262 characters can only occur if there is a fault. The causes here can be a defective active participant on the respective segment or dynamic interference on the segment.

In addition, a start bit and telegram length check is carried out as a monitoring mechanism. A counter is increased by two if an invalid start delimiter or a valid start delimiter with an inappropriate telegram length is detected. The counter is decreased by one for each error-free telegram received until it reaches the counter reading of zero again. The start bit and telegram length check outputs an error signal if the counter reading exceeds a predefined number. This detects errors in which the telegram has been corrupted by a defective participant or interference.

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A repeat error test as a further monitoring mechanism is intended to prevent a formally valid telegram from circulating forever in an optical single-fiber ring if the device 74 for the telegram start test is no longer able to take the telegram from the optical single-fiber ring. The repeat error test contains a counter that is increased by one if the second character of a telegram just received matches that of the previous telegram or if a single-character telegram is received. If there is a discrepancy, the counter is set to zero, as is the case if a new telegram is fed into the monitored single-fiber ring. In the latter case, the device 74 for the telegram start test is also active again. The repeat error test also outputs an error signal if the counter reading exceeds a predefined number. The repeat error test detects, for example, interference coupling into an open optical fiber or into the transceiver.

The switch 64 interrupts the forwarding of received telegrams for echo filtering and is triggered by the device 74 for the telegram start test with a signal on a line 81. In the event of an error that was detected by the ring monitoring 78, the switch 64 can also be opened by the ring monitoring 78. The switch 64 is only closed again when the segment is idle in the send and receive directions.

All monitoring mechanisms can be activated individually or in combination with each other through parameterization.

When coupling devices are connected to an optical ring, each optical channel must remove the telegrams it has fed into the ring from the ring again so that no endlessly circulating telegrams are created. The device 74 for the telegram start test therefore remembers one character from up to 32 telegrams sent, which enables the optical channel to

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light, to recognize the telegrams it has fed into the optical ring and to remove them from the ring by opening switch 64, as already described above. The received telegrams are constantly compared with the sent telegram beginnings already stored in the device 74 for the telegram beginning test. If the received telegram beginning matches the oldest entry, it is deleted. If the telegram beginning does not match the oldest but one of the younger entries, it is assumed that the older telegrams have been disrupted. In this case, the matching and all older entries are deleted. The device 74 for the telegram beginning test blocks the forwarding of received telegrams by opening switch 64 until all entries have been deleted and the end of the telegram whose beginning matches the last entry has been reached. If more than 32 entries are to be stored in the device 74 for the telegram start test, the device 74 reports an overflow to the ring monitor 78. The ring monitor 0 78 then interrupts the sending and receiving of telegrams on the optical channel for one ring cycle time.

The delay element 75, which contains a shift register, delays the received telegrams after the RXD machine 62 so that they only arrive at the device 74 for the telegram start test when an identifier of the original telegram, of which the received telegram represents the echo, has been registered in the device 74 for the telegram start test via line 70. In the device 74, the sequence can therefore always be followed: first send a telegram and store the identifier of the telegram, then wait for the echo and recognize it as an echo based on the identifier.

The device 86 for an activity check monitors activities on the connected segment. If no bus activity is detected for a predefined period of time

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can, this is reported by a signal on a line 82 to the segmentation logic 71, which then triggers a decoupling of the relevant segment. Monitoring is carried out using a counter that is reset with each signal change on line 61 and otherwise counts continuously. If a specified counter reading is exceeded, the report signal is sent to the segmentation logic 71 and the counter reading is reset. When determining the specified time period, the maximum possible signal runtime in the network between the most distant bus participants must be taken into account in order not to limit the network expansion by a time threshold that is too small.

Any of the following events can trigger a segment disconnection:

1. A received CRC check character is not adapted to the received telegram or a stop bit error occurs in a received telegram character,

2. the optical signal level on the optical fiber has fallen below a minimum value; this is indicated to the segmentation logic 71 by a level measuring device through a signal 120,

3. the memory provided in the device 74 for the telegram start test overflows if more than 32 telegrams are sent without receiving a valid echo,

4. no activity is detected on the receiving line 61 for a predefined monitoring time or

5. a monitoring mechanism of the ring monitoring 78 detects errors in a received telegram.

The basic process of segment decoupling is explained using the flow chart in Figure 6, using the example of a fault on segment 15 in Figure 2. After a reset, the sequence control is in a basic state 90 in which the switch 64 is closed. If an event causes a

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If segment decoupling is initiated, the basic state 90 is initially left and a wait state 91 is entered, in which the switch 64 is opened and forwarding of received telegrams to connected segments 12 and 16 is blocked. An error is displayed, but an error message is not yet sent via the signal contact. In the wait state 91, a predeterminable minimum segmentation period is waited for, which is preferably longer than the time threshold of a timer in the device for activity check, which monitors transmission pauses on the connected segment and triggers segment decoupling if exceeded. This ensures that the neighboring coupling device, in the embodiment according to Figure 2 the coupling device 21 adjacent to the coupling device 22, has also triggered segment decoupling, i.e. also blocks the forwarding of telegrams received from segment 15 to the other connected segments 11 and 14 before special telegrams are exchanged in a state 92 to check segment 15. The special telegrams are generated in the segmentation logic (Figure 5) and sent to segment 15 via the AND gate 76 and a transceiver (not shown). State 92 is referred to as first check. The longer the waiting time in state 91, the lower the influence of low-frequency dynamic interference on the network.

On the other hand, the waiting time for segments connected in series with coupling devices determines how long the line is interrupted at least after a fault.

When segment 15 is disconnected, switches 64 and 73 are open. This means that no echo is formed and the forwarding of received telegrams is blocked. However, the RXD machine 62, the device 77 for determining the telegram length and the CRC check 63 remain active in order to carry out an assessment of the transmission quality based on received telegrams and to communicate the result of the assessment to the segmentation logic 71 via lines 79 and 80.

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In the wait state 91, the system reacts to received special telegrams and leaves the wait state 91 in order to be able to react to special telegrams from the neighboring coupling device 21, which is already in the first check state 92. After receiving a special telegram, 22 bit times are waited for, which correspond to maintaining the minimum telegram distance of eleven bit times and ending a possibly just started character, before the first special telegram is sent in the first check state 92.

As already described above, one reason for segment disconnection can be that a timer for monitoring transmission activities on the segment has exceeded a preset maximum idle time. The reasons for this can in turn be a break in the fiber optic cable or a failure of the neighboring coupling device. Another possibility for this time monitoring to be triggered is to switch off all active participants in the network. The disconnected segment can therefore be OK or faulty if the maximum idle time is exceeded. Before an error message is issued, the relevant segment is therefore checked by exchanging special telegrams in the first check state 92. If this first attempt to exchange special telegrams without errors fails, the coupling devices connected to the segment switch to a cyclic check state 93 in which they cyclically attempt to transmit special telegrams and at the same time activate an LED and a signaling contact to indicate the error. The signaling contact can be wired to an operating and monitoring station to generate an error message. This measure enables automatic visualization of a fault. If special telegrams are transmitted without errors in both directions, the system switches to basic state 90 and segment 15 is automatically connected to the network again. The special telegrams implement a handshake procedure that ensures that the locks in both coupling devices 21 and 22 on segment 15 are released at the same time.

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This advantageously prevents only one transmission direction from being activated at certain times. The segment therefore allows bidirectional transmission immediately after coupling. If there is no data traffic on the segment after this, the timer for monitoring the maximum idle time is activated again and an exchange of special telegrams is initiated again without an error message being issued. The exchange of special telegrams in the First Check state 92 is indicated by a flashing LED and thus serves as an operating display as long as there is no data traffic on segment 15. In contrast, in the Cyclic Check state 93 an error is indicated by the LED lighting up continuously and an error message is issued via the signaling contact. The segment decoupling is maintained in this state. In the Cyclic Check state 93, special telegrams are sent to the faulty segment at predeterminable cyclic intervals and a check is carried out. If the special telegrams are transmitted correctly, the cyclic check state 93 returns to the basic state 90 and the error message is removed. To implement the handshake procedure with special telegrams, two special telegrams STl and ST2 were introduced, which are sent cyclically until the segment is reconnected. The special telegrams differ from the useful telegrams that are transmitted in the network so that they cannot be interpreted as such. In addition, a parity bit with a polarity that is reversed compared to the parity bit in useful telegrams is used for the telegram characters in the special telegrams. The special telegram STl is used to cyclically initiate a check of the segment, while the special telegram ST2 is sent as confirmation of correct telegram transmission. The special telegrams are provided with a CRC check character to check the transmission quality.

The flow chart in Figure 7 illustrates the procedure of a segment coupling with transmission of special telegrams.

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men. The vertical areas corresponding to the wait state 91, the first check state 92 and the cyclic check state 93 in Figure 6 are marked by vertical lines on the right side in Figure 7.
5

After a segment has been uncoupled, the system switches to state 100, in which a timer is started to monitor a minimum segmentation time. If the timer has expired, the system switches to state 101 and a special telegram STl is sent. The expiration of the timer is marked by a state transition arrow 102. State 101 is also entered, as indicated by an arrow 103, if a special telegram STl or a special telegram ST2 has been received. After sending a special telegram STl in state 101, the timer for monitoring the minimum segmentation time is reset and restarted when it switches to state 104. If no special telegram STl or ST2 is received from the coupling device adjacent to the segment before the timer expires, the system switches to state 105, as indicated by an arrow 106, and a special telegram STl is sent again. If, however, a special telegram STl was received before the timer expired in state 104, a transition to a state takes place according to an arrow 107.

108, in which a special telegram ST2 is sent. The timer is then reset and in a subsequent state

109 is started again. If in state 109 no response telegram is received from the neighboring coupling device during the timer expiration for the special telegram ST2 sent, the system switches to state 105 according to an arrow 110, which represents the start of the cyclic check. If, on the other hand, a special telegram ST2 sent by a neighboring coupling device has arrived within the monitoring time, this means that the receive and send path of the segment are OK, and the system switches to state 112 according to an arrow 111, in which the segment is reconnected, i.e. the forwarding of received telegrams to neighboring segments is enabled. In state 105,

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which was taken after the timer expired, the coupling device sends a special telegram STl to the faulty segment again. A cycle timer is then reset and a state 113 is entered, in which the expiration of the cycle timer is monitored. The monitoring time of the cycle timer determines the cycle duration with which special telegrams are sent to the segment. If the cycle duration has expired without receiving a special telegram, the system returns to state 105 as indicated by an arrow 114.

If, however, a special telegram ST1 sent by a neighboring coupling device was received, a transition to state 116 takes place according to an arrow 115, in which a special telegram ST2 is sent to the neighboring coupling device. The cycle timer is then reset and the expiration of the cycle timer is monitored again in state 117. If the cycle timer expires without a special telegram ST2 being received, the system returns to state 105 according to an arrow 118. Receiving a special telegram ST2 sent by a neighboring coupling device in state 117 means that the receive and send paths of the segment are OK again, and the system switches to state 112 according to an arrow 119, in which the cyclic check is completed and the segment is coupled again. State 112 corresponds to the basic state 90 in Figure 6.

Using the handshake procedure shown with special telegrams ST1 and ST2, a faulty segment is automatically and easily reconnected once the faults have been eliminated.

Segments that must comply with a specific protocol, for example PROFIBUS DP, which does not allow special telegrams, are released again without such a handshake procedure. In the example shown in Figure 2, segments 11, 12 and 13 are such segments. Here, the respective coupling device also releases the corresponding

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faulty segment is decoupled, i.e. the forwarding of telegrams that were received on the faulty segment 11, 12 or 13 is blocked. The FIFO memory of the retimer is deleted. After a parameterizable minimum segmentation time has expired, a monitoring timer and a telegram counter are started. When the segment is decoupled, sending to the faulty segment remains enabled in order to prevent the formation of subnetworks, which - as already described above - could result in the formation of double tokens, for example. The forwarding of telegrams received on segments 15 or 16, for example, to segment 12 therefore remains even if segment 12 is faulty and is independent of whether the forwarding of telegrams in the opposite direction is blocked. Monitoring mechanisms check the received signal of the faulty segment. The monitoring timer is reset and restarted each time a signal is received. If no further telegrams are received within the monitoring time, then there are probably no participants connected to the segment and a temporary interference trigger has been triggered. The segment can therefore be reconnected. If a predefined number of error-free telegrams are received in succession before the monitoring time expires, the segment is reconnected as soon as the segment is idle in the transmit and receive directions.

Based on the example in Figure 8, a possibility will be described below of achieving a higher availability of the network by connecting the components to form an optical double ring. In the network shown, participants 201 ... 206 are each connected to coupling devices 221 ... 226 by segments 211 ... 216 with electrical signal transmission, on which data is transmitted according to the PROFIBUS DP protocol. The coupling devices 221 ...

226 are connected in pairs by segments 231 ... 236 with optical signal transmission, so that an optical double ring is created, as shown in Figure 8. The

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Segments 231 ... 236 have optical fibers 241 ... 246 or optical fibers 251 ... 256 that can be operated independently of one another for each transmission direction. The coupling devices 221 ... 226 monitor segments 211 ... 216 and 231 ... for interference and decouple disturbed segments, as already described using the network shown in Figure 2. When a disturbed segment is decoupled, for example segment 236 in Figure 8, the original optical double ring becomes an optical line in which the participants 201 ... 206 can still be reached. This increases the availability of the network. By exchanging special telegrams between the coupling devices, in the example of a faulty segment 236 between the coupling devices 221 and 226, the elimination of the fault is detected in the manner already described above and the segment 236 is reconnected to the network after the fault has been eliminated. After the fault has been eliminated, the optical line is thus closed again to form an optical double ring.

The functional principle of the optical double ring is that telegrams that are fed in by a subscriber via a segment with electrical signal transmission are forwarded by the coupling device simultaneously to both connected segments with optical signal transmission. For example, a telegram that the subscriber 201 sends via the segment 211 to the coupling device 221 is forwarded by the coupling device 221 both via the optical fiber 251 of the segment 231 to the coupling device 222 and via the optical fiber 246 of the segment 236 to the coupling device 226.

This results in a duplication of the telegram sent by the subscriber 201. The two circulating, completely identical telegrams are then recognized as identical telegrams by the coupling device 224, where they meet due to the transit time, and are taken from the optical double ring. The device 74 (see Figure 5) is used for this purpose for the telegram start test, which stores a character to identify sent telegrams in order to, as already mentioned above,

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was written to prevent telegrams from circulating forever. The mechanisms described ensure that the telegrams circulating in opposite directions are removed from the optical double ring even if the two telegrams meet in a segment with optical signal transmission, i.e. not directly at a coupling device.

If segment 236 has been disconnected due to interference from coupling devices 221 and 226, a telegram from subscriber 201 is simply forwarded to segment 231 by coupling device 221 and is therefore not duplicated. Before reconnecting a faulty segment with optical signal transmission, it can also happen that some of the two identical telegrams circulating in the optical double ring in opposite directions are erased at the coupling device that blocks the forwarding of telegrams to the faulty segment, while the telegrams that have a longer transit time to the coupling device opposite the faulty segment are still on the way. In this case, the balance of identical telegrams circulating in opposite directions is disturbed. If, in the event of an imbalance in circulating telegrams, a faulty segment were to be reconnected after the fault had been eliminated, circulating telegrams could arise in the optical double ring, which can be detected and eliminated, but which will disrupt the entire network until they are eliminated.

A simple way to avoid the occurrence of such circulating telegrams is to enable a segment after the fault has been eliminated at a time when no telegrams are in transit on the network. In a network with participants that handle data traffic according to the PROFIBUS DP protocol, this state is certain to occur shortly afterwards when an active participant has sent a so-called GAP query to a participant that is not present in the network. In PROFIBUS DP, active participants with GAP queries cyclically carry out

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klich checks whether new participants have been connected to the network and want to participate in the data traffic. With each GAP query, the querying participant waits for a response with which the new participant reports, provided that it has been connected to the network in the meantime. If the querying participant does not receive a response within a predefined time, the so-called slot time, it assumes that the queried participant cannot be reached on the network. The slot time is calculated so that it is longer than the longest possible time delay between the query and response telegram. It is the sum of the runtimes of the query telegram to the queried participant and the response telegram to the querying participant between the participants furthest away from each other, plus a response delay from the queried participant and a safety margin.

The coupling devices 221 226 require for certain transmission

monitoring mechanisms, e.g. for setting the monitoring time in the device 8 6 (see Figure 5) for the activity check, information about the network extent. One way to communicate this information to the coupling devices would be to parameterize them via the network.

However, this option would involve a lot of effort, as the coupling device would have to appear as a separate, addressable participant when the network is being planned. Another option would be to make the network expansion manually adjustable or readable on the coupling devices. However, this option would be prone to errors and would involve a lot of effort when installing the network. The network expansion could also be preset in the coupling devices using a default value, which would have to be designed for the maximum permissible network expansion and would be unnecessarily high for the respective application in a network.

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The slot time is advantageously measured by the coupling devices 221 ... 226 during operation of the network. The slot time contains information about the network expansion, so that complex parameterization of the coupling devices with regard to the network expansion can be omitted. The slot time Ts is parameterized in the participants as follows:

L = T^ +2

S * ^X SM ^TÄ I '"gas U _n . K * ^Bit

with

Ts - slot time,
Tsm - a safety surcharge,

Ltotal - sum of the lengths of the segments with optical signal transmission,

N _K - number of coupling devices,
V _K - signal propagation time through a coupling device, Tsdx - maximum possible delay time after which a called participant must respond to a call telegram, and

Tßit - the duration of a bit at the currently set data rate.

The slot time is therefore designed to be at least twice as long as would actually be necessary for the network expansion. The slot time is then also longer than the maximum delay in an optical line to which the optical double ring in Figure 8 is split if, for example, a fault is detected on segment 236 and segment 236 is disconnected.

To ensure that no telegrams circulate in the network when a blocked segment is re-enabled after the fault has been eliminated, the coupling devices involved must wait for a GAP query from an active participant and then for half the slot time to elapse. After receiving

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of a GAP query telegram, half the slot time must also be waited for, since in the case of a GAP query to a participant present in the network, its response telegram would reach the coupling device before half the slot time has elapsed. If no response telegram arrives at the coupling device after a GAP query within half the slot time, it must have been a GAP query to a participant that is not present and there are certainly no telegrams in the network. This procedure avoids circulating telegrams in the optical double ring when segments are coupled after the fault has been eliminated.

Since the coupling devices 221 ... 226 can only measure the slot time when active participants send GAP queries to participants that are not present in the network, the HSA (Highest Station Address) of the active participants is configured so that GAP queries are made to at least one non-existent participant during operation. So that the slot time is determined exclusively on the basis of such GAP queries, the measurements are only made between two call telegrams with acknowledge or between a call telegram with acknowledge and a token telegram. So that the measured slot times can be automatically adjusted when the network changes or so that incorrect measurements can be corrected, the slot time measurements are carried out continuously during operation. The measurement is made with a slot time counter that counts the number of bit times between the end of a call telegram with acknowledge and the start of the subsequent telegram. The determined slot time is stored in a slot time marker in the slot time determination 51 (see Figure 4). As an initial value after a restart of the network, the slot time marker in the coupling devices is set to a default value that corresponds to the highest adjustable value. After each valid measurement, the slot time marker is overwritten with the new measured value.

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Active participants are participants who are in the network's logical token ring and can therefore accept the token and pass it on to the next active participant in the logical token ring. The respective token holder has the right to send to the network. In contrast, passive participants cannot accept the token. They only send response telegrams when they have been requested to do so by a token holder via a request telegram.

Claims (3)

GR 98 G 4445 DE 31 Protection claims 1. Coupling device for connecting at least two segments in a network in which several participants (4, 5, 7, 8) are connected to one another for data transmission, characterized in that more than two channels (41 ... 44) are present for connecting one segment each to the coupling device and that at least one channel can be switched off independently of the other channels of the coupling device in order to reduce energy consumption. 2. Coupling device according to claim 1, characterized in that the channels (41 ... 44) each contain a retimer (62, 65, 66) in order to compensate for distortions of a received telegram. 3. Coupling device according to claim 1 or 2, characterized in that means are provided to generate a signal with which the respective channel is switched off in the absence of a circuit for adapting signals received on a segment to the logic circuit of a switchable channel.