CH641919A5 - Data transmission device - Google Patents

Description

641 919

PATENT CLAIMS

1. Data transmission device, with a data modem with a plurality of inputs / outputs (16) which can be connected to corresponding data inputs / outputs by assigned devices (12), which assigned devices (12) have a command signal for each input / output which represents a request to allocate transmission capacity to the relevant data input / output, characterized by means (103) for multiplexing the inputs / outputs (16) in one of several assignments and for selecting a commanded input / output -Assignment under the influence of control signals, and means (19, 21, 17) for automatically detecting a change in the command signals, which requires a transition to a new input / output assignment, and for automatically controlling the switching of the multiplexing means (103 ) to the new input / output assignment.

2. Data transmission device according to claim 1, characterized in that the inputs / outputs (A, B, C, D) are assigned priorities from 1 to N, that the number of input / output assignments is N and that said determination means (19, 21, 17) are set up to cause the multiplexing means (103) to choose the input / output assignment in which the input / output which has the last priority and for which a command signal is present, Transmission capacity is allocated.

3. Data transmission device according to claim 1, characterized in that said determining means (19, 21, 17) contain means (36, 31, 37) for comparing the command signals with a code signal that the current one caused by the multiplexing means (103) Displays input / output assignment, and to determine the need for a transition to a new input / output assignment from the comparison.

4. Data transmission device according to claim 3, characterized in that the command signals are encoded and that the comparison means (36, 31,37) contain means (37) for storing one of a plurality of code signals which the current input / output assignment of the multiplexing means ( 103), and for replacing this code signal with another one of the code signals under the action of second control signals, and means (36, 31), to which said one code signal and the command code signal are fed, for determining necessary changes in the input / output -Assignment and for generating said second control signals depending on this determination.

5. Data transmission device according to claim 4, characterized in that said plurality of code signals and the command code signals are in different code types and that the means (36, 31) to which said one code signal is supplied, means (36) for converting the code signals and which have command code signals in a common code type and thus for generating a first and a second code signal in the common code type, and a comparison circuit (31), to which the first and second code signals in the common code type are supplied, for generating the said second control signals.

6. Data transmission device according to claim 4 or 5, characterized in that the second control signals contain a control signal of the first type, which indicates that an input / output is to be activated, and a control signal of the second type, which indicates that an input / output is to be deactivated, and a third-type control signal which indicates that the current input / output assignment is the input / output assignment represented by the current command code signal.

7. The data transmission device as claimed in claim 6, characterized in that the means (37) for storing is a shift register which supplies the said plurality of code signals at its output and which, under the action of the control signal of the first type and the control signal of the second type, which / Output assignment representing code signal changes at its output.

8. Data transmission device according to claim 7, characterized in that the shift register (37) is pushed by the control signal of the second type and the control signal of the first type inputs a code signal into the shift register (37), which indicates that all inputs / outputs (A, B , C, D) transmission capacity is allocated.

9. Data transmission device according to claims 5 and 8, characterized in that the means (36, 31) to which the said one code signal is supplied have means (33, 35) for delaying the control signal of the first type and the control signal of the second type.

10. Data transmission device according to claim 9, characterized by means (57, 59, 41) for optionally switching over to operation as a controlling station or as a controlled station.

11. Data transmission device according to claims 5 and 8, characterized in that the means (36,31), to which said code signal is supplied, have a locking circuit (39) which responds to the control signal of a third type in order to hold a new command code signal .

12. Data transmission device according to claim 1, characterized in that said determining means (19, 21, 17) are set up to determine changes in command signals which take the form of standard connection establishment signals from the modem.

13. Data transmission device according to claim 12, characterized in that said determination means (19, 21, 17) are set up to determine changes in command signals which have the form of send request signals (RTS).

14. Data transmission device according to claim 12, characterized in that said determining means (19, 21, 17) are set up to determine changes in command signals which have the form of data carrier detection signals (DCD).

15. Data transmission device according to claim 12, characterized in that said determination means (19, 21, 17) are set up to determine changes in command signals which have the form of data terminal ready signals (DTB).

16. Data transmission device according to claim 5, characterized in that the code signals representing the input / output assignment are in binary form and that the means (37) for storing the one of a plurality of code signals are set up to convert the stored code signal in each case to change a bit when inputs / outputs are to be deactivated and to pass to a code signal which indicates that all inputs / outputs have transmission capacity allocated when inputs / outputs are to be activated.

Modems for digital data for the arrangement between data processing devices and the two ends of a transmission line, e.g. a telephone line are known. Modems with a plurality of inputs / outputs are also known which have a plurality of channels for connection to a corresponding plurality of channels of the assigned2

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provide data processing equipment. Multiplexing transmits the multi-channel information over a single line. Multiplexing is usually done by time division multiplexing (TDM), the channels being nested bit by bit. Various multiplexing methods are of course known and could be used in connection with the invention.

For the establishment of a connection via a transmission line between modems, it is known to generate a sequence of connection establishment signals. These signals can indicate when a data source actually wants to transmit data or wants to have a channel ready for transmission. An example of the first possibility are send command signals or ready to send signals (RTS). An example of the second option are data terminal ready signals (DTR) or (DSR). Send command signals are only present as long as a transmission is in progress, while data terminal ready signals are present throughout the time that the data source is in information exchange with a device such as e.g. a central process computer (CPU). The generation of data carrier detection signals (DCD) and receive line signal detection signals (RLSD) is also known. It is known not only the generation of DCD when a data carrier occurs from a connected modem, but also the downshifting of DCD when receiving a coded inverse RTS signal (RTS). A commercially available modem that uses the signals described above is the "Milgo 96 MM" modem. These signals can be used advantageously in connection with the invention.

Known modems with several inputs / outputs contain the necessary circuits for switching between different input / output distributions depending on the control, which are set manually by an operator. Such channel allocation or change in input / output distribution is useful when traffic patterns change relatively infrequently and in a known manner. It is then possible to draw up an operating mode switchover plan which, from time to time, requires the operator to act to effect operating mode changes. Of course, the activities of two operators, each setting a modem at each end of the transmission line, must be coordinated. In order to enable better use of the expensive telephone channels, it would be desirable to have means for "dynamically changing the input / output distribution, by means of which the data processing device and the modem for the rapid and automatic change of the input / output distribution without the action of a Operator work together.

It is therefore an object of the invention to enable the change in the input / output assignment in a modem without manual action.

The object is achieved with the data transmission device defined in claim 1.

If an assigned device with data inputs / outputs that are connected to the inputs / outputs of the data modem requires a change in the input / output (channel) assignment, the corresponding command is determined. It can be held and an indication of it can be communicated over a transmission line to serve as an input / output reassignment command in a second modem. Preferably after a suitable time delay which allows the second modem to switch to the requested input / output assignment, the first modem, to which the input / output reassignment command was originally supplied by the assigned device, can then switch to the new one Switch input / output assignment. The data modem or the multiplexer at that end of the line from which the command for a new input / output assignment originates is referred to as the controlling station, while the multiplexer modem at the other end of the line is the controlled station. The switching of the operating mode or input / output assignment takes place as required, so that if a data source does not require transmission capacity, the transmission capacity in question can be allocated to the active data sources.

A preferred embodiment of the invention is explained below with reference to the drawings.

1 is a simplified block diagram of a system with data transmission devices according to the preferred embodiment of the invention.

Figure 2 is a block diagram of a channel allocation circuit.

Figure 3 illustrates the input / output assignment dialing sequence in the preferred device.

Fig. 4 shows in the form of a flow diagram the activity of the device when deactivating channels.

Fig. 5 shows the activity of the device when activating previously inactive channels.

Figure 6 shows in general form a block diagram of an input / output assignment selector circuit in the preferred device.

Fig. 7 is a schematic of an input / output assignment selector circuit that can be used in both the controlling station and the controlled station.

1 shows two modems (modulation and demodulation devices) 11 and 13, which are connected to one another via a transmission line 15. A data processing device is connected to each of the modems 11 and 13, e.g. a central process computer, a data terminal or another peripheral device. For example, the modem 11 is connected to several inputs / outputs 16 of a central process computer 12, while the modem 13 is connected to several inputs / outputs of data terminal equipment 14.

A plurality of modems having inputs / outputs, in which a plurality of channels, which emanate from assigned data processing devices, are combined using a multiplex method for transmission via a line, are known. For example, a modem can combine four inputs / outputs, each of which transmits 2400 bits per second, resulting in a total data frequency of 9600 bits per second. In the other modem connected to the transmission line, the information of the individual channels is then separated again. Typically, the transmission equipment includes a four-wire line for simultaneous transmission in both directions, with multiplexers and de-multiplexers being at both ends of the line.

In practice, it is often desirable to rearrange the distribution of the channels or the inputs / outputs. If, for example, two channels are not required for the transmission of data in a device with four inputs / outputs at a given time, it is desirable to switch these two channels off or to allocate the bandwidth used by them to the channels via which they are active is transmitted. In this way, the transmission line can be better used.

As already indicated, known modems with several inputs / outputs contain the necessary circuits for switching between different input / output distributions in response to manually entered commands. A typical method for encoding the data in a multiple

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Transmitter having inputs / outputs is shown in FIG. 2. 2 is somewhat simplified; however, those skilled in the art will readily understand the circuit design.

2, the bandwidth allocation in a four-channel system is determined by a clock selection circuit 101, which selects the clock signals which are supplied to each of four multiplex demultiplexing circuits 103. The clock selection circuit 101 is fed by a clock signal generator 105 and contains frequency dividers and logic circuits in order to generate four divided clock signals which are interleaved in a cyclic, four-phase clock signal sequence ®i, O2, <I> 3, d> 4. The clock signal phases are selectively supplied to the multiplex demultiplexing circuits 103 as a function of an instruction code which has been set manually in known modems. The mutually phase-shifted output signals of the circuits 103 are combined by an OR gate 104 to form a signal at 9600 bits per second on a single line. The OR gate 104 delivers this signal at 9600 bits per second to a transmitter 106 of the modem, where the data signal is modulated according to known methods.

If, for example, of four channels A, B, C, D only the two channels A and B are required for the transmission of data, two clock signal phases are supplied to the multiplexer circuits for these channels A and B, which means that the data frequency in these channels A and B is doubled while the other two channels, C and D, are inactive.

A possible way of interleaving the data bits at different data frequencies is shown in Table A below.

Table A

Fre- Be data frequency in the data compilation mode, channel type

A B C D

9600

2nd

4800

4800

- Ao, Bo, Al, Bl, A2, B2, A3 B3, A4, B4, A5, BS, A6, B6 AV, B7

9600

4th

2400

2400

2400

2400 Ao, Bo, Co, Do, Ai, Bi, Ci Dl, A2, B2, C2, D:, A.l, B3

9600

4th

7200

2400

- Ao, A i, A2, Bo, A3, A4, Aï BI, A6, AT, AS, B2, A9, Aio, All, B3

9600

5

4800

2400

2400

- Ao, Bo, AlCo, A2, Bl, A3, Cl, A4, B2, A5, C2, A6, B3 A7, C3

7200

2,4,5

4800

2400

-

- Ao, Al, Bo, A2, A3, Bl, A4 A5, B2, AÖ, A7, B3

7200

3rd

2400

2400

2400

- AO, BO, CO, AI, BI, CI, A2, B2, C2, A3, B3, C3

4800

2,3,5

2400

2400

-

- Ao, Bo, Ai, Bi, A2, B2, A3

Bs

In the preferred embodiment of the invention, a channel distribution or input / output distribution command is supplied in coded form to a modem 11, which operates as a controlling modem in a data transmission system, from a connected data processing device, for example the central process computer 12. The current input / output distribution is controlled by code stored in a mode shift register 17 (or other storage device). The code stored in the shift register 17 selects the input / output distribution in the same way as that in known ones

Modems with multiple inputs / outputs manually entered command code. A comparison circuit 19 continuously compares the input / output distribution command supplied by the process computer 12 with the command stored in the operating mode shift register 17. If the process computer 12 requests an input / output distribution other than that stored in the shift register 17, then the comparison circuit 19 generates control signals for the shift register which indicate a new operating mode code to be stored in the shift register 17. After a suitable delay by a delay circuit 21, these control signals serve to change the operating mode code stored in the shift register 17 and thus to effect a new input / output distribution in the modem 11.

The delay caused by the delay circuit 21 has the purpose of providing a sufficient time period in which the second or controlled modem 13 can also respond and switch over to an input / output distribution which corresponds to the newly commanded input / output distribution in the controlling modem 11 corresponds. During this period, the controlling modem 11 sends signals to the controlled modem 13 which are interpreted by the modem 13 as a transmitted input / output distribution command. With devices that function similarly to those in the controlling modem 11, the input / output distribution is then also switched in the controlled modem 13. In particular, a comparison circuit 23 determines the new input / output distribution command by comparing the command code with the code stored in a shift register 25. The comparison circuit 23 generates control signals for the shift register which, after a suitable delay, change the operating mode code stored in the shift register 25 in order to change the input / output distribution in the modem 13.

The devices described with reference to FIG. 1 are preferably designed in such a way that a channel priority order and a predetermined redistribution order result, with which the circuits are simplified and existing orders in the modem can be used. The order in which the input / output distributions or operating modes are selected preferably corresponds to that shown in FIG. 3 and Table I below.

Table I

Frequency channel request operating mode input / output distribution

A

B

c

D

A

B

C.

D

9600

1

X

X

1

3rd

24th

24th

24th

24th

9600

1

X

1

0

5

48

24th

24th

9600

1

1

0

0

4 or 2

72

24th

9600

1

0

0

0

1

96

7200

1

X

1

X

3rd

24th

24th

24th

7200

1

1

0

5

48

24th

7200

1

0

0

1

72

4800

1

1

X

X

23

24th

24th

4800

1

0

1

48

Table I shows various input / output distributions with different data frequencies as an example. For the following description, the data frequency 9600 bits per second has been selected as an example. The table specifies the channel request or the operating mode code, which consists of four bits, which are assigned to the four inputs / outputs or channels A, B, C and D. The code consists of «1», «0» and «indifferent», the latter represented by the character «X». The one operating mode code ent5

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speaking input / output distribution is indicated in the same line as the operating mode code. In addition, each operating mode is arbitrarily assigned one of the numbers 1 to 5.

According to Table I, in mode 3, data is transmitted at 2400 bits per second on each of channels A, B, C and D. In mode 5, channel D has been omitted, as indicated by the “0” in column “D” of the mode code. Channels B and C transmit 2400 bits per second, while channel A operates at 4800 bits per second. If only channels A and B are in operation, one of the two operating modes 4 or 2 can be selected. In mode 4, channels A and B operate at 7200 and 2400 bits per second, respectively, and in mode 2, they operate at 4800 bits per second. In mode 1, the mode code indicates that only channel A should work, and this channel A then works at 9600 bits per second.

According to Table I, the channels are assigned priorities that decrease from channel A to channel D. The channel with the lowest priority that is still in operation dictates the operating mode. For example, the choice of operating mode 3 depends only on whether channel D is working or not, but not on whether channels B and C are shown as working or not. Channel A is the channel with the first priority, in it the data frequency increases continuously when other channels are omitted.

As already indicated, the channels required by a newly supplied command code are expediently compared in the automatic devices for input / output distribution with the existing channel activation signals. When inputs / outputs need to be added or omitted, control signals are generated which cause the remote (controlled) modem to switch in the same way as the local (controlling) modem. Both modems are controlled so that they run through the different operating modes in the same order in order to arrive at the correct input / output distribution. In the preferred embodiment, the order is determined according to the schedule shown in FIG. 3. According to this plan, a modem that works in one of the 5.4, 2 or 1 operating modes can simply add the necessary channels to return directly to operating mode 3. However, in order to move to another of the operating modes in the order upwards, for example from operating mode 1 to operating mode 5, it is first necessary to return to operating mode 3 before operating mode 5 can be reached. It's also going through the order from top to bottom, i.e. when switching from a higher operating mode to a lower operating mode, it is essential to go through any intermediate operating modes. This switching plan is advantageous because it enables the simplification of the information transmission that is necessary for effecting operating mode changes in the controlled or remote modem.

This communication uses a failure of a volume detection signal in the controlled modem to cause the loss of a channel in the controlled modem. According to the plan already explained, it is always the input / output with the last priority that determines when a channel should be deleted. Since a channel that has been dropped is no longer used at all, there is no easy way to return directly to an operating mode in which this channel is active, because the time intervals for this channel have been allocated elsewhere.

Therefore, in the preferred embodiment, when a channel is to be reactivated, the input / output distribution devices always return to mode 3, in which all channels are active, and then omit the unnecessary channels until the desired one

Operating mode is reached. Since channel A is always active, a failure of the volume detection signal for that channel is used to represent and trigger a return to the highest mode, mode 3. Starting from operating mode 3, failures of the data carrier detection signals of other channels are then used for further switching to the desired operating mode.

An example of the switching order just described is shown in FIGS. 4 and 5. In this example, the signal «DTB» (= «data terminal ready») is used as a command code in the controlling modem, which is initially set to operating mode 3 and then switches to operating mode 1 and then to operating mode 5.

4 illustrates the omission of channels from operating mode 3 to operating mode 1. Initially, the controlling modem is in normal idle operating mode 3, in which, according to Table I, the signals “DTB” for channels A and D are logical 1. The controlled modem is similar in idle mode 3, with the data carrier detection signals of channels A and D being logic 1. The controlling modem initiates a transition to operating mode 1 if the signals «DTB» for channels B, C and D go to zero at the same time. First there is a delay of 200 ms during which the failure of the data carrier detection signals of channels B, C and D is transmitted to the controlled modem. In the controlled modem there is a delay of 100 ms for determining the failure of the data carrier detection signals and triggering the switchover to operating modes 5 and 4 and finally to operating mode 1. The intermediate operating modes, in example 5 and 4, are preferably run quickly , as indicated by the time information 0.416 ms in FIG. 4. Because of the greater delay in the controlling modem, the controlled modem reaches operating mode 1 before the controlling modem switches to operating mode 1. This ensures that the controlled modem is ready for operation in the new operating mode of the controlling modem in good time. In the same way, any desired number of inputs / outputs can be omitted. When the controlling modem switches back to operating mode 1, normal data transmission on the single channel A is then started at 9600 bits per second.

5 illustrates the addition of channels when switching from mode 1, in which only channel A operates, to mode 5, in which channels A, B and C operate. Initially, the controlling modem is in operating mode 1, whereby the «DTB» signal for channel A is positive. The controlled modem in operating mode 1 is similar, with the data medium detection signal for channel A being positive. The transition to operating mode 5 is triggered when the signals «DTB» for channels B and C are switched on. This begins the delay time of approximately 200 ms, during which the controlling modem sends only "characters" to the controlled modem, which indicates that the data carrier detection signal for channel A has failed. With the detection of this failure, the delay time of 100 ms begins in the controlled modem, during which the controlled modem switches to operating mode 3, in which all four channels operate. Again, due to the different delay times, the controlled modem reaches operating mode 3 before the controlling modem.

After the controlling modem has reached operating mode 3, it determines that operating mode 3 is not yet the right one, since the «DTB» signal for channel D is low.

Thereafter, the procedure shown in FIG. 4 is essentially followed in order to omit channel D and to go to operating mode 5. The failure of the data carrier detection signal for channel D is sent to the controlled modem

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transmitted, after which the controlled modem switches to operating mode 5 after a delay. The delay in the controlling modem is greater, so that the controlling modem switches to operating mode 5 after the controlled modem and then normal data transmission at 4800 bits per second via channel A, at 2400 bits per second via channel B and at 2400 bits per second on channel C. 5 shows how to return to the mode in which all channels are active in order to add inputs / outputs.

As described above, the "DTB" signal and the data carrier detection signal are used, because these signals are used very often anyway in the transmission between modems. The operating mode codes supplied to the controlling and the controlled modem could, however, also be represented by other signals. For example, a signal "send request" could just as well be used in the controlling modem to indicate the operating mode code instead of the "DTB" signal.

As already mentioned, a request signal can be used to indicate when a data source actually wants to transmit data or wants to have a channel available for the transmission. A signal that is often used for the first-mentioned display is the “send request” signal. The "DTB" signal (= "data terminal ready") is often used for the second display. Which of these signals is used as a request signal from a data source largely depends on the type of data source. If the data source, e.g. a tape reader of the type which mainly sends out data in longer blocks of a few minutes, which alternate with longer periods of rest, the signal “send request” is normally suitable as a request signal. This “send request” signal is only present as long as a transmission is in progress, and the use of the “send request” signal therefore enables the bandwidth required to be reallocated during the idle periods during which the data source is not providing any data and the “send request” signal is not available is.

However, this procedure is usually not suitable if the data source is one that is actively exchanging data with another device, e.g. a data processing terminal; Because such a source often switches quickly between data transmission and silence, and the resulting frequent change in the operating mode would not be desirable. In this case the request signal is preferably a «DTB» signal which is present all the time the data source is connected to the device at the controlled end of the line, e.g. a process computer that is actively connected. A redistribution of the bandwidth will only occur if the data source switches off the "DTB" signal because it no longer wants to maintain the connection to the process computer.

As already mentioned, it is known not only to generate a volume detection signal when a volume from the controlling modem occurs, but also to turn off the volume detection signal when an encoded send request is received. A common format for the encoded transmit request is a series of louder 1 for a predetermined period of time, which in the case of channels B, C and D can be approximately 200 ms. However, it is also possible to send a specific code word to the coded transmission request.

The controlled modem determines the coded transmission request in channels B, C and D. As described above, the effect is delayed to allow a reliable determination (because otherwise the determination could be made incorrectly as a result of a longer series of louder 1s that occur during normal data transmission).

FIG. 6 shows a simplified block diagram of a circuit for controlling the input / output distribution in a controlling or controlled modem in the manner described above with reference to FIGS. 3 to 5. The circuit contains a size comparator 31, two timers 33 and 35 and a shift register 37 indicating the operating mode. The size comparator 31 compares the inverted channel activation signals of channels B, C and D, which are supplied by the shift register 37 indicating the operating mode, with the inverted signals. DTB »of the relevant inputs / outputs in the controlling modem or with the inverted data carrier detection signals of the relevant inputs / outputs in the controlled modem. The channel activation signals are generated by converting the code appearing at the shift register output in a decoding circuit 36. The input signals of the size comparator 31 are marked overall with X and with Y bb.

The relationship between X and Y indicates the type of channel distribution change required. For example, if it is necessary to switch from operating mode 1 to operating mode 5, the ABCD signal Olli is present at the X input, while the ABC D signal 0001 is present at the Y input. In this case, with X> Y, the display of the operating mode 3 is automatically entered into the shift register 37. The signal causing the input of operating mode 3 is delayed in timer 35; the timer generates the delay described above with reference to FIGS. 4 and 5. On the other hand, if X is less than Y, it follows that a channel should be omitted. In this case, the shift register 37 is simply switched on to the next operating mode code, again after the suitable delay which is caused by the timer 33. If after a step X <Y is still present, the shift register 37 is switched on again in order to reach the next operating mode. When X = Y finally, there is an idle state in which the active channel distribution corresponds to the commanded operating mode. So the importance of the comparison is to determine whether channels should be added or dropped. Instead of the size comparator 37, various other logic circuits could of course also be used to make this determination on the basis of the channel activation signals and the command code.

Fig. 7 shows a more detailed schematic of a preferred circuit which can control the input / output distribution in both a controlling modem and a controlled modem. The reversal for operation in a controlling or a controlled modem is carried out by means of a reversing device which controls a multiplexer, as described in detail below.

When operating in a controlling modem, the control signals, e.g. the signals “DTB” from four inputs / outputs to a four-bit locking device 39. The content of this locking device 39 is fed via a multiplexer 41 to a logic circuit 43 which responds to the signal for the channel of the last priority and then to a comparator 45. The comparator compares the channel activation signals at the X inputs with the output signals of the logic circuit 43 and supplies control signals to a shift timer 47 or an input timer 49. These two timers are connected via a multiplexer 51 to a shift register 53 indicating the operating mode. The output signal of the comparator 45 occurring in the idle state at X = Y is fed to a locking controller 55 which controls the operation of the locking device 39.

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A changeover device 57 serves to change over the entire circuit for operation in a controlling modem or for operation in a controlled modem. In a controlling modem, the multiplexer 41 is caused to supply the output signals of the four-bit locking device 39 to the logic circuit 43. In a controlled modem, the multiplexer 41 supplies the logic circuit 43 with the data carrier detection signals “DFS” received via a bus. The reversing device 57 also ensures that the multiplexer 51 in the controlling modem supplies the output signals of the shift timer 47 and the input timer 49 delayed by 200 ms to the shift register 53. In the controlled modem, on the other hand, the multiplexer 51 forwards the output signals of these timers delayed by 100 ms. The multiplexers, which are of a known type, contain controlled switches or gates.

When operating in a controlling modem, the locking device 39 normally samples the input signals in rapid succession. However, if a change in state is determined so that the quiescent state output of comparator 45 no longer indicates X = Y, then locking controller 55 controls locking device 39 in such a way that

that this locks and holds the newly ordered operating mode display.

The interlock controller 55 includes an AND gate 59, an inverting AND gate 61 and a delay flip-flop 63. The AND gate 59 is supplied with an input signal indicating X ^ Y and an input signal indicating operation in the controlling modem. When these two input signals occur, the output signal of the AND gate 59 is high and the output signal of the flip-flop 63 reset in the idle state is also high. In this case, the inverting AND gate 61 provides a low output signal which indicates the locked state and blocks an AND gate 65 for sampling clock signals. If, on the other hand, X = Y or if the circuit is not set to operate in a controlling modem, the output signal of the AND gate 61 is high and indicates the scanning operating state for the locking device 39.

The delay flip-flop 63 is used to control the processes during the switchover to operating mode 3. For such a switchover, the signal “DTB” of channel A changes (it fails as described above) in order to send the required information to the controlled modem to transmit. So that the comparator 45 does not simply determine X # Y and hold the low "DTB" signal of channel A, the flip-flop 63 is set by an input command and then prevents the locking until the "DTB" signal again assumes its initial state (high). According to F.ig. 7, the flip-flop 63 is supplied with clock signals with the baud frequency for this purpose and the input command and its reset input are fed the signal “DTB” of channel A to its D input.

The locking device 39 therefore has the task of preventing all interruptions and changes in the input signals until the circuit for controlling the input / output distribution has completely processed all the preceding changes. In this way, the necessary control signals are generated and the controlled modem is transmitted and followed there before later commands for new input / output distributions can take effect.

The code selected by the multiplexer 41 is then fed to the logic circuit 43 responsive to the signal for the channel of last priority, in which the signal for the channel of last priority receives priority in the sense that it signals the signals for the channels of higher priorities in the active ones Condition. This essentially replenishes the "equally valid" states in Table I. The channel A

relevant information is not influenced by the logic circuit 43. The mode of operation and thus the structure of the logic circuit 43 are shown in Table II below.

Table II

input Output

(Send request / data (to the comparator) *

carrier detection) *

A

B

c

D

A

B

c

D

A

X

X

0

A

0

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* inverted logic!

As already mentioned, the size comparator 45, which can be a commercially available digital comparator, provides output signals for X> Y, X <Y and X = Y. The output signal X = Y indicates that a commanded channel distribution is equal to the channel distribution with which is just being worked. This lock state or X = Y output signal of the comparator 45 controls the lock controller 55. If X ¥ *, the lock is initiated. The output signal occurring at X <Y is fed to the shift timer 47, which delivers a shift command to the shift register 53 after a delay time selected by the multiplexer 51 in the manner described. The output signal occurring at X> Y is fed to the input timer 49 and, after the delay time selected by the multiplexer 51 has elapsed, the code for the operating mode 3 is input into the shift register 53. The shift timer and the input timer can be standard counter circuits.

After receiving a shift command from the shift timer 47, the shift register 53 changes its initial states in rapid succession until the comparator 45 determines equality. This logic function is represented in FIG. 7 by an AND gate 50 which, in response to the shift signal from the timer 47, supplies the shift register 53 with clock signals until the comparator 45 emits the idle state output signal. If, after entering operating mode 3, there is no equality X = Y, the output signal for X <Y appears, which causes the shift register just described to be shifted.

If the shift register 53 is not in the shift or input state, then it simply holds the respective operating mode display at its outputs. The operating mode display can be fed to a reversible device which chooses between operating mode 2 and operating mode 4.

In summary, it can thus be stated that, in operation in a controlling modem, when a new channel distribution is commanded, the comparator 45 issues either a shift command or an input command. These commands are delayed by timers 47 and 49, respectively. During the delay time, signals are transmitted over the channel to the controlled modem. In particular, if channels are to be omitted, this is determined at the output of the four-bit locking device 39 and the corresponding command code is transmitted. The output signals of the locking device are fed via lines 40 to a device for transmitting the command code, which device can be of a known type. If operating mode 3 is to be entered, then

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the corresponding command is transmitted on a line 42 to the controlled modem after the input display has been determined by the comparator 45. At the end of the delay time defined by the timer 47 or 49, the shift command or the input command is forwarded to the shift register 53. The operating mode specified by the shift register is then fed back to the comparator 45, which determines whether a further change in the content of the shift register is required or whether equality X = Y has been reached.

When operating in a controlled modem, the locking device 39 is switched off by the multiplexer 41. The mode of operation is otherwise the same, with the exception that the data carrier detection signals “DFS” are supplied to the logic circuit 43 and the comparator 45. The timer multiplexer 51 selects the shorter delay time and a command represented by the volume detection signal must be present for the duration of a timer cycle for the circuit to respond.

Instead of the one described, other methods could also be used to synchronize the switching of the channel distribution in the physically separate modem. In such a method, for example, a secondary channel operating with frequency sampling or a complete channel could be used for the transmission of the synchronization information

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independent data transmission path can be used. Such an independent data transmission path could be provided within the data transmission devices or in external devices.

In another method, the synchronization of two modems could be effected by a user by commanding a switchover of the input / output distribution at predetermined times for both modems at the same time. For example, at the end of the day, the devices, such as computers or data terminals, assigned to the 10 individual, physically separate modems, can provide a predetermined channel for the specific information transmission. Since the device controlling the modem has a control clock signal source in each station, the synchronization according to these control clock signal sources is a simple matter. Because of the synchronous control clock signal sources in all stations, no signal transmission from one modem to another is required. Rather, the modems can be configured to follow the commands provided by the data terminal equipment. In this way, a user can directly control the input / output distribution according to programs by providing his own synchronization codes.

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3 sheets of drawings