EP2380064A1

EP2380064A1 - Device and method for the automated detection of an interface

Info

Publication number: EP2380064A1
Application number: EP09756280A
Authority: EP
Inventors: Elmar Mayer; Alexander Kobler
Original assignee: Dr Johannes Heidenhain GmbH
Current assignee: Dr Johannes Heidenhain GmbH
Priority date: 2008-12-18
Filing date: 2009-11-03
Publication date: 2011-10-26
Also published as: US10120359B2; CN102257446A; US20110258358A1; JP5279920B2; DE102008054887A1; WO2010069664A1; DE102008054887B4; JP2012513017A; CN102257446B

Abstract

The present invention relates to a device and to a method for the automated detection of an interface between a position measuring device (10) and a downstream electronic unit (110), which are interconnected by way of a data transmission channel (100), wherein the position measuring device (10) comprises an interface unit (20) and a position measuring unit (30). The interface unit (20) is connected, first, to the data transmission channel (100) and, secondly, to the position measuring unit (30) for the purpose of internal data exchange. In the interface unit (20), the interface to the downstream electronic unit (110) can be selected from at least two interfaces. In the position measuring device (10) there is also an interface detection unit (200), which receives at least one input signal (E1, E2), arriving from the downstream electronic unit (110) by way of the data transmission channel (100), and which comprises means for defining the chronological sequence of signal edges of the at least one input signal (E1, E2) in conjunction with the signal state, and to an evaluation unit (260), in which the interface to the downstream electronic unit (110) can be detected by evaluating the chronological sequence defined and can be selected in the interface unit (20).

Description

Device and method for automated recognition of an interface

The invention relates to an apparatus and a method for the automated detection of an interface between a position measuring device and a subsequent electronics according to claims 1 or 9. By means of such a device, or a method according to the invention, in the position measuring device is an automated detection of the Subsequent electronics used interface possible.

In automation technology, more and more position measuring devices are used which provide an absolute position value. This eliminates certain disadvantages of so-called incremental position measuring devices, such as e.g. the need to make a reference movement after switching on to find a reference position that serves as a reference point for further position measurement by counting graduation marks.

For the transmission of the absolute position values mainly serial data interfaces are used, since they manage with only a few data transmission lines and nevertheless have high data transmission rates. Particularly advantageous here are the so-called synchronous serial interfaces, which have a unidirectional or bidirectional data line and a clock line. The transmission of data packets over the data line is synchronous with a clock signal on the clock line. In automation technology, a variety of standard interfaces has prevailed, popular representatives for synchronous serial interfaces, for example, the EnDat interface of the applicant, another is known under the designations SSI. In addition, asynchronous serial interfaces such as Hiperface are also common.

The SSI interface is described in EP0171579A1. It is a synchronous-serial data interface with a unidirectional data and a unidirectional clock line. Reading out positives Onswerten of a position measuring device takes place here in synchronism with a clock signal on the clock line.

By contrast, EP0660209B2 describes the basis of the Applicant's EnDat interface. This is also a synchronous-serial interface, which has a bidirectional data line in addition to the unidirectional clock line. This allows transmission of data in both directions - from the sequential electronics to the position measuring device and from the position measuring device to the subsequent electronics. The data transmission also takes place here synchronously with a clock signal on the clock line.

DE19701310B4 describes a device for data transmission between a transducer designed as a position measuring system and a processing unit. By transmitting a reference signal on one of the signal transmission lines, via which the data transmission between the transducer and the processing unit takes place, the position measuring system can be switched to different operating modes.

Standardized interfaces offer the advantage that measuring devices equipped with such an interface can be connected directly to subsequent electronics, for example a machine tool control system. However, it is disadvantageous for the measuring device manufacturer that he has to offer the measuring devices with different standard interfaces in order to be able to offer solutions for subsequent electronics which are already equipped with a specific interface. This results in a large variety of variants, which requires a great deal of effort in product maintenance and makes storage considerably more difficult.

JP8185591A describes an absolute position measuring device that supports multiple transmission formats. The selection of the transmission format via a selection signal, which is supplied to the position measuring device via additional lines of the subsequent electronics. The requirement to provide additional lines increases the cabling complexity. wall considerably and is therefore undesirable. In addition, this solution is inflexible because the transmission format must be set manually.

It is therefore an object of the invention to provide a device and a method with which the interface can be detected by the position measuring device.

This object is achieved by a device according to claim 1. Advantageous details of the device result from the claims dependent on claim 1.

A device is now proposed for the automated detection of an interface between a position measuring device and a subsequent electronic unit, which are connected to one another via a data transmission channel, wherein the position measuring device comprises an interface unit and a position measuring unit. The interface unit is connected to the data transmission channel on the one hand and to the position measuring unit for the purpose of exchanging data on the other hand. In the interface unit, the interface to the subsequent electronics can be selected from at least two interfaces. The position measuring device further comprises an interface recognition unit which is supplied with at least one input signal arriving from the sequential electronics via the data transmission channel and which comprises the means for determining the time sequence of signal edges of the at least one input signal in conjunction with the signal state, and an evaluation unit in which, by evaluating the determined time sequence, the interface used for the subsequent electronics can be recognized and selected in the interface unit.

Further, this object is achieved by a method according to claim 9. Advantageous details of the method emerge from the dependent of claim 9 claims.

A method is proposed for automated recognition of an interface between a position measuring device and subsequent electronics, - A -

which are interconnected via a data transmission channel, wherein the position measuring device comprises an interface unit and a position measuring unit. The interface unit is connected to the data transmission channel on the one hand and to the position measuring unit for the purpose of data exchange on the other hand. In the interface unit, the interface to the subsequent electronics can be selected from at least two interfaces. In the position measuring device, an interface recognition unit is furthermore arranged, which is supplied with at least one input signal which arrives from the subsequent electronics via the data transmission channel. The method according to the invention comprises the following steps:

Determining a time sequence of signal edges of the at least one input signal in conjunction with a signal state,

- Determination of the used interface to the subsequent electronics by evaluation of the determined sequence on the basis of decision criteria in an evaluation unit and

Selection of the determined interface in the interface unit.

Further advantages and details of the present invention will become apparent from the following description of a device or a method for automated detection of an interface with reference to the figures. It shows

FIG. 1 shows a block diagram of a device according to the invention,

FIG. 2 a shows a data transmission channel with a line pair operated unidirectionally and a bidirectionally operated line pair,

FIG. 2b shows a data transmission in unidirectionally operated pairs of lines, in the case of data transmissions, FIG.

FIG. 2c shows a data transmission channel with a bidirectionally operated line pair, FIG. 3 is a block diagram of an interface recognition unit;

4a shows a signal diagram of the beginning of a data transmission at the interface EnDat and FIG. 4b shows a signal diagram of the beginning of a data transmission at the interface SSI.

1 shows a block diagram of a device according to the invention with a position measuring device 10, which is connected via a data transmission channel 100 with a subsequent electronics 110, for example a numerical machine tool control (NC). Position measuring device 10 and subsequent electronics 110 exchange commands and data via the data transmission channel 100. In most cases, such a system is a master-slave connection, with the sequential electronics 10 taking over the function of the master and the position-measuring device 10 assuming the function of the slave, i. Each data transmission is initiated by the subsequent electronics 1 10, while the position measuring device 10 transmits data only on request to the subsequent electronics 1 10. As an interface, the physical connection between subsequent electronics 1 10 and position measuring device 10 for the purpose of data transmission (represented by the data transmission channel 100) in conjunction with the associated rules, the so-called. Interface protocol referred to.

The data transmission channel 100 is usually designed for serial data transmission, ie it consists of at least one serial data connection, which, if the transmission is differentiated according to RS-485 standard, consists of at least one line pair and is completed on both sides with suitable driver / receiver modules , If the transmission takes place via only one bidirectionally operated differential pair of lines, this is also referred to as a 2-wire interface. A popular example of this is the parameter channel of the Hiperface interface. In contrast, the EnDat and SSI interfaces mentioned in the introduction use two differential line pairs and are thus referred to as 4-wire interfaces. By way of example, termination resistors R1, R2, R3 are also shown in FIG which are used to attenuate signal reflections on the lines. In practice, 10 terminating resistors R1, R2, R3 can be provided both on the side of the position measuring device 10, as well as on the side of the subsequent electronics. Differential data transmission has long been known to the person skilled in the art and will not be described further here.

The position measuring device 10 should be suitable in this example for the automated detection of 2-wire interfaces and 4-wire interfaces. In addition, the two possible signal line pairs should be usable and thus interchangeable. The variants shown in FIGS. 2a to 2c must be taken into account here:

a unidirectionally operated line pair, a bidirectionally operated line pair (FIG. 2a) - two unidirectional lines operated in different data directions

Signal line pairs (FIG. 2b)

a bidirectionally operated signal line pair (FIG. 2c)

In order to enable the interchangeability, the two signal line pairs of the data transmission channel 100 on the side of the position measuring device 10 are each terminated with a differential transmitter / receiver pair. On the side of the subsequent electronics 1 10 only the receiver / transmitter modules are present, which requires the interface used.

The data transmission channel 100 is connected in the position measuring device 10 with an interface unit 20, the commands and input data from the subsequent electronics 1 10 receives, interprets and forwards via an internal interface to a position measuring unit 30. The latter processes commands and input data and, if output data, for example an absolute position value, has been requested, transmits these via the internal interface to the interface unit 20, which processes the output data in accordance with the interface protocol and sends it to the sequential electronics 110. The position measuring unit 30 generates position signals by scanning a measuring standard with a scanning unit and converts these into digital position values which indicate the absolute position of the scanning unit relative to the measuring scale. The physical principle on which the scanning is based is not relevant here; for example, optical, magnetic or inductive measuring principles can be used. In addition to position values, further data can be generated in the position measuring unit 30. These include, for example, further measured values resulting from the relative movement between the scanning unit and the material measure, such as speed or acceleration. The other data can also be measured values that relate to the environmental conditions, eg temperature values. Finally, status information can also be made available as further data, for example in the form of status bits or a status word whose bits signal warning or error states.

The position measuring unit 30 may include other components, such as a CPU for performing complex calculations, and a memory unit, the representation of which has been omitted here. Access to the components arranged in the position measuring unit 30 or the data exchange with these components takes place via the interface unit 20.

The internal communication in the position measuring device 10, which takes place between the interface unit 20 and the position measuring unit 30 via the internal interface, is largely independent of the interface protocol, which determines the communication between subsequent electronics 1 10 and position measuring device 10 via the data transmission channel 100. In order to allow the fastest possible data exchange between the interface unit 20 and the position measuring unit 30 via the internal interface, parallel data transmission is preferably used here. Thereby, the time between the arrival of a command over the communication channel 100 and the transmission of requested data (eg the position value) via the communication channel 100.

The interface unit 20 is switchable, i. the interface unit 20 offers a choice of at least two interfaces, for example EnDat and SSI, from which one can be selected. In this way, the position measuring device 10 can be connected to subsequent electronics 1 10 support either SSI or EnDat interfaces. It is obvious that position measuring devices 10, which support a multiplicity of different interfaces, drastically reduce the necessary variety of variants, since they support many subsequent electronics 110 without any effort by simply selecting an interface that supports both the subsequent electronics 110 and the position measuring device 10 will be able to be connected.

The interface unit 20 is preferably of modular construction and offers specific interface modules 22.1, 22.2 for the supported interfaces. to 22. n, of which according to the interface used by the subsequent electronics 1 10 one is selected. In addition to the specific interface module 22.1, 22.2. to 22. n is advantageously a general interface module 23 is provided with the specific interface modules 22.1, 22.2. to 22. n communicates via a standard interface 24. As a result, the functional scope of the specific interface modules 22.1, 22.2. to 22. n on the implementation of the received from the sequential electronics 1 10 commands and input data to a standardized Befehlsbzw. Data format, as well as the conversion of output data from a standardized data format to a specific data format for transmission to subsequent electronics 1 10 are reduced.

In the position measuring device 10, an interface detection unit 200 is arranged for automated detection of the connected interface, the input signals E1, E2 are supplied, which arrive via the data transmission channel 100. Of course, the number of input signals is limited to two only in this embodiment. In the In practice, both interfaces are known, having only one input signal, as well as interfaces that transmit more than two input signals. Detection occurs, as will be further explained below, by analyzing the timing of signal edges and levels of the input signals. As long as the interface has not been detected, the connection of the interface unit 20 to the data transmission channel 100 is interrupted. For this purpose, a switching unit 215 is provided. In addition, the driver blocks, which are provided for the transmission of data to the subsequent electronics 1 10, inactive, so it will be analyzed exclusively via the data transmission channel 100 incoming signals. After successful recognition of the interface, the interface detection unit 200 correspondingly switches over the interface unit 20, for example via a selection line 210, or selects a specific interface module 22.1, 22.2 to 22. n and establishes the connection between the interface unit 20 and the data transmission channel 100 Switching unit 215 restored.

In order to ensure that the interface has also been recognized correctly, it makes sense to provide a test sequence after detection which is suitable for reliably detecting the data transmission between subsequent electronics 110 and position measuring device 10.

Advantageously, the automated recognition of the interface is limited to a special programming mode of the position measuring device 10, in which the position measuring device 10 is located after delivery. After the successful detection of the interface during the commissioning of the position measuring device 10 to the subsequent electronics 1 10, the result is stored in a non-volatile memory, such as an EEPROM, or the selected specific interface module 22.1, 22.2. to 22. n, so that once the interface used has been detected, no further automatic detection is required. Subsequently, the programming mode is ended. Furthermore, a special mechanism can be provided to switch the position measuring device 10 again into the programming mode. For example, the switching to the programming mode, as proposed in DE19701310B4, by a Reference signal, which is transmitted on one of the signal transmission lines of the data transmission channel 100 from the sequential electronics 1 10 to the position measuring device, initiated.

Based on the block diagram of an interface recognition unit 200 according to the invention shown in FIG. 3, the automated interface recognition will now be further explained. The input signals E1, E2, which arrive at the interface detection unit 200 via the data transmission channel 100, are supplied to edge detection units 220, 221. These encode signal states or transitions of the respective input signal E1, E2 on each of two status lines whose digital signal levels are assigned to the four states or transitions - low level high level - rising edge falling edge and a control unit 240, as well as a state memory unit 230 are supplied. In a further refinement, the edge detection units 220, 221 also recognize the state "tri-state" or "high-resistance".

If the control unit 240 detects an edge in one of the input signals E1, E2, it evaluates the event as the beginning of a data transmission and starts a recognition sequence by starting a timer 250 via a start line 241 and the digital signal levels of the status lines, as well as the value of the timer 250 by means of a write line 242 in the state memory unit 230 stores. This store operation is repeated for a specified number of signal edges. In this way, the state memory unit 230 is filled with data records which contain signal states or transitions of the input signals E1, E2 and the times associated therewith, so-called time stamps. Alternatively, the timer 250 can also be started immediately after switching on, for example after a switch-on reset process. If the timer 250 is only started once and then counts continuously, the time between two signal edges or up to to the first signal edge (when timer 250 is already started after power up), by forming the difference between two timer values. If, on the other hand, the timer 250 is restarted for each detected signal edge, then the timer value directly corresponds to the time between two signal edges.

The number of data records required depends on how many and which interfaces are to be detected. At least as many data records must be recorded that exactly one interface can be determined unambiguously from all interfaces in question. In order to produce a redundancy, it is particularly advantageous to record additional data records, so that a check / confirmation of the determined interface is possible.

If a sufficient number of data records have been recorded, the control unit stops the timer 250 and signals via an evaluation line 243 of an evaluation unit 260 that it can evaluate the data records. The data sets are evaluated by analyzing the time sequence of the signal transitions (edges) and the associated signal states and comparing them with characteristic signal sequences of available interfaces, which are stored in a database 270, for example. The evaluation may include testing for one or more of the following decision criteria:

- Signal level before the first signal edge

- Detection of a clock signal Determining the frequency of a clock signal

Detection of asynchronous data transmission Identification code identification Consideration of signal levels of a second input signal

Signal edges of a first input signal

An identification code may, for example, be a pulse sequence which, irrespective of the actual execution of the Interface (synchronous / asynchronous, number of input signals ...), which allows selective selection of an interface. The validity of the identification code is advantageously limited to the programming mode.

As a special case, it should be mentioned here that the absence of signal edges, ie the determination that a defined time after switching on or the beginning of the recognition process, the input signals E1, E2 have a constant logic level, can serve as a decision criterion.

Which decision criteria for the unique recognition of the interface used are expedient, depends on the type and number of available, or to be recognized interfaces. If, for example, only two interfaces are to be distinguished which have different quiescent levels, the consideration of the signal levels before the first clock edge is sufficient. The decision whether it is a synchronous or an asynchronous interface can be made after the detection of a clock signal or a characteristic signal sequence. To distinguish between two synchronous interfaces, the consideration of the signal levels of the second input signal at signal edges of the (already recognized) clock signal can be used.

After recognition of the interface used, the evaluation unit 260 selects the corresponding interface via the selection line 210.

Alternatively, the evaluation can also be carried out without prior intermediate storage by supplying the data records directly to the evaluation unit 260. In this case, however, a high processing speed is required in the evaluation unit 260.

Based on the figures 4a and 4b will now be explained using the example of the recognition of the interface used, if only between the interface SSI and EnDat must be distinguished. FIG. 4a shows the beginning of a data transmission from the sequential electronics 110 via the data transmission channel 100 to the position measuring device 10 using the interface EnDat, which is described for example in EP0660209B2. After switching on, the first input signal E1 is at high level, the level of the second input signal E2 is low. The first input signal E1 in this example corresponds to the signal on the clock line, while the second input signal E2 represents the signal on the bidirectionally operated data line.

The transmission begins with a falling edge of the first input signal E1, while the second input signal E2 is in the output state, ie immediately after switching, high impedance (tri-state) is connected. In the high-resistance state, a voltage sets in on the second signal line E2 which is determined by the termination resistors R1, R2, R3. These are, as mentioned above, needed in digital data transmission to attenuate signal reflections. The termination resistors R1, R2, R3 are usually dimensioned such that the resulting voltage on the second signal line E2 is interpreted by the receiving side, in this case the position measuring device 10, either as a high level or a low level, wherein the termination resistors R1, R2, R3 are preferably dimensioned so that the position measuring device 10 detects a high level. With the third falling edge, the sequential electronics 1 10 starts transmitting a command (referred to in the terminology of EP0660209B2 as a status command). This consists of three consecutively transmitted bits, which are then repeated in inverted form. In an alternative embodiment of the EnDat interface, however, the repetition of the command can also take place in the same polarity.

By contrast, FIG. 4b shows the signal states at the beginning of a data transmission at the SSI interface which, as already mentioned in the introduction, is described in EP0171579A1. Assuming that the first input signal E1 is the signal on the clock line and the second input signal E2 is the signal on the data line, there is first input signal Nal E1 in the initial state also to high level and the data transfer begins with a falling edge of the first input signal E1. Since in SSI the data line is operated unidirectionally by the position measuring device 10 to the subsequent electronics and the driver components are inactive during the automated detection of the interface, the second input signal E2, regardless of the input signal E1 always remains at the same level, in turn of termination resistors R1, R2, R3 is determined. In the example shown, the second input signal E2 has a constant low level.

In the evaluation unit 260, the clock line can now be identified by the fact that the signal on this line (in the example, the first input signal E1) has further edges at regular time intervals after the first edge.

The detection of the clock line is not sufficient in this example as a decision criterion for the determination of the interface used, since it is in both cases to synchronous interfaces. Here, for example, the consideration of signal levels of the second input signal E2 at signal edges of a first input signal E1 (the clock signal) can be used as a further decision criterion. Since no level change can occur on the data line in the case of the SSI interface, but a command is transmitted in the case of the EnDat interface, and the logic level on the data line therefore changes, an unambiguous determination of the interface is possible. A previous level change at the time , in which the second input signal E2 is switched to high impedance in FIG. 4a, is unreliable as a decision criterion since it depends on the dimensioning of the termination resistors R1, R2, R3.

In this way, decision criteria can be found for a large number of different interfaces, which enable the evaluation unit 260 to perform automated recognition. For example, a sequence of signal edges at irregular intervals would be an indication of a Asynchronous interface over which an ASCII-coded character is transmitted.

It goes without saying that the access from the sequential electronics 110 to the position-measuring device 10 during the automated recognition of the interface, in that the position-measuring device 10 neither sends nor receives data, leads to transmission errors on the part of the subsequent electronics 110. However, since the automated detection takes place outside the actual operation of the position measuring device 10, this is not problematic.

In addition, it may happen that a single interface access is not sufficient for a clear recognition of the interface. Thus, in Figure 4a, assuming that the idle state at the second input signal E2 is a low level, in the tristate state, the level on the termination resistors R1, R2, R3 is also set to low level, the transmission of a command with the level sequence '000' is coded and repeated only in the same polarity, likewise do not generate a level change. A safe decision between SSI and EnDat could not be made in this case.

Such combinations can be avoided if a person who carries out the commissioning of a machine are used in the position measuring devices 10 according to the invention, in a commissioning instruction the interface commands to be used for automated detection are specified. If necessary, the instruction to use several different interface commands, if a first attempt did not succeed, is already sufficient.

Claims

claims

1. A device for automated recognition of an interface between a position measuring device (10) and a subsequent electronics (1 10), which are connected to one another via a data transmission channel (100), wherein the position measuring device (10) an interface unit (20) and a position measuring unit ( 30), the interface unit (20) is connected to the data transmission channel (100) on the one hand and to the position measuring unit (30) for the purpose of exchanging data, the interface to the subsequent electronics (1 10) in the interface unit (20). is selected from at least two interfaces and in the position measuring device (10) further an interface detection unit (200) is arranged, the at least one input signal (E1, E2), which from the subsequent electronics (1 10) via the data transmission channel (100) arrives, and the means for determining the time sequence of signal edges of the at least one input signal (E1, E2) in conjunction with the signal state and an evaluation unit (260) in which the interface used for the subsequent electronics (1 10) can be identified and selected in the interface unit (20) by evaluating the determined time sequence.

2. Apparatus according to claim 1, wherein the means for determining the time sequence of signal edges of the at least one input signal (E1,

E2) in conjunction with the signal state comprise at least one edge detection unit (220, 221) for detecting signal edges and signal states, and a timer (250) for determining the time sequence of the signal edges.

3. Device according to one of claims 1 or 2, wherein in the interface detection unit (200) further a state memory unit (230) is arranged, which supplied the detected signal edges and signal states, and connected to the signal edges timer values and in which these values can be stored.

4. Device according to one of the preceding claims, wherein during the automatic detection of the interface, the connection between the interface unit (20) and the data transmission channel (100) is interrupted.

5. Device according to one of the preceding claims, wherein the interface unit (20) comprises at least two specific interface modules (22.1, 22.2, ..., 22. n), each associated with an interface and the selection of the interface in the interface unit (20 ) by selecting a specific interface module (22.1, 22.2, ..., 22. n).

The apparatus of claim 5, wherein the interface unit (20) further comprises a general interface module (23) connected to the specific interface modules (22.1, 22.2, ..., 22, n) via a standard interface (24) ,

7. Device according to one of the preceding claims, wherein the position measuring device (10) for automated detection of the interface in a programming mode is switchable.

8. Device according to one of the preceding claims, wherein the selection of the interface can be stored after the detection.

9. A method for automated detection of an interface between a position measuring device (10) and a subsequent electronics (1 10), which are connected to each other via a data transmission channel (100), wherein the position measuring device (10) has an interface unit (20) and a position measuring unit (30) the interface unit (20) is connected to the data transmission channel (100) on the one hand and to the position measuring unit (30) for the purpose of internal data exchange, wherein in the interface unit (20) the interface to the subsequent electronics (110) consists of at least two interfaces is selectable and in the position measuring device (10) further an interface detection unit (200) is arranged, which at least one input signal (E1, E2) which arrives from the sequential electronics (110) via the data transmission channel (100), the method comprising the following steps: determining the time sequence of signal edges of the at least one input signal (E1, E2) in connection with the signal state,

- Determining the interface used to the subsequent electronics (110) by evaluating the sequence determined by decision criteria in an evaluation unit (260) and - Selection of the determined interface in the interface unit (20).

10. The method of claim 1, wherein the detection of signal edges and signal states of the at least one input signal (E1, E2) in at least one edge detection unit (220, 221) takes place and the time sequence of signal edges of a timer (250) is detected.

11. The method according to claim 9, wherein the detected signal edges and signal states as well as the timer values connected to the signal edges are stored in a state memory unit (230) which is likewise arranged in the interface recognition unit (200).

12. The method according to any one of claims 9 to 1 1, wherein during the automatic detection of the interface, the connection between the interface unit (20) and the data transmission channel (100) is interrupted.

13. The method according to any one of claims 9 to 12, wherein the interface unit (20) comprises at least two specific interface modules (22.1, 22.2, ..., 22. n), each associated with an interface and for selecting the interface in the interface unit (20) one of the specific interface modules (22.1, 22.2, ..., 22. n) is selected.

14. The method according to any one of claims 9 to 13, wherein the position measuring device (10) for automated detection of the interface is switched to a programming mode.

15. The method according to any one of claims 9 to 14, wherein the selection of the interface is stored after recognition.