Test circuit and industrial device

Abstract

A test circuit (11) comprises a supply terminal (12), a reference potential terminal (13), a first number N of digital terminals (14 - 16) and a first number N of switches (17 – 19), a supply input terminal (35), and a support resistor (37). The support resistor (37) is coupled to the supply terminal (12) and to the supply input terminal (35). A switch (17) is coupled to the supply terminal (12) and to a digital terminal (14). An industrial device (50) comprises a supply line (51), a reference potential line (73), a control circuit (52), a second number M of device terminals (53 – 55) and a presence detector (83) coupled to the supply line (51) and to the reference potential line (73). The presence detector (83) is configured to detect a first value of a supply voltage (US1) at the supply line (51) when the presence detector (83) is in a high resistive state, and a second value of the supply voltage (US1) when the presence detector (83) is not in a high resistive state.

Description

[0001] Description

[0002] TEST CIRCUIT AND INDUSTRIAL DEVICE

[0003] The disclosure relates to a test circuit , an industrial device and an arrangement with a test circuit and an industrial device .

[0004] The test circuit is configured to be connected to the industrial device . The test circuit is designed to generate signals which are applied to the industrial device . The test circuit and the industrial device are two separate parts . The test circuit simulates an application in which the industrial device is embedded . The test circuit generates signals and provides the signals to the industrial device . The test circuit could be reali zed as a pattern generator, signal generator or function generator . However, such generators are expensive and require a lot of space and electrical power .

[0005] It is an obj ective to provide a test circuit , an industrial device and an arrangement with a test circuit and an industrial device that can be implemented with low ef forts .

[0006] This obj ect is achieved by the subj ect-matter of the independent claims . Further developments and embodiments are described in the dependent claims .

[0007] The definitions as described above also apply to the following description unless otherwise stated .

[0008] In an embodiment , a test circuit comprises a supply terminal , a reference potential terminal , a first number N of digital terminals and a first number N of switches . A switch of the first number N of switches is coupled to the supply terminal and to a digital terminal of the first number N of digital terminals .

[0009] Advantageously, the test circuit is designed to generate signals by switches which electrically couple or decouple the supply terminal to the first number N of a digital terminals . Thus , a digital terminal of the first number N of a digital terminals can be set on a voltage provided at the supply terminal or is left unconnected .

[0010] In an embodiment of the test circuit , a switch of the first number N of switches couples the supply terminal to a digital terminal of the first number N of digital terminals .

[0011] In an embodiment , the test circuit comprises a supply input terminal and a support resistor . The support resistor is coupled to the supply terminal and to the supply input terminal . In case , a current flowing through the support resistor is zero , an input voltage provided at the supply input terminal and a supply voltage provided at the supply terminal are equal . In case , the current flowing through the support resistor is not zero , the input voltage and the supply voltage provided at the supply terminal are di f ferent .

[0012] In an embodiment of the test circuit , the first number N is at least one , two , three , four, five or six . For example , the first number N is in a range between 2 and 20 or in a range between 4 and 14 or in a range between 6 and 8 .

[0013] In an embodiment of the test circuit , a switch of the first number N of switches is implemented as a manually operated electromechanical device . Each switch of the first number N of switches is implemented as a manually operated electromechanical device .

[0014] In an embodiment of the test circuit , a switch of the first number N of switches is implemented as one of a toggle switch, a rotary switch, a push-button switch, a dual inline package switch ( abbreviated DIP switch) and a rocker switch .

[0015] In an embodiment , the test circuit comprises an analog terminal and a voltage divider . The voltage divider includes a first terminal , a second terminal and a divider tap . The first terminal of the voltage divider is coupled to the supply terminal . The second terminal of the voltage divider is coupled to the reference potential terminal . The divider tap of the voltage divider is coupled or connected to the analog terminal of the test circuit .

[0016] In an embodiment of the test circuit , the voltage divider is manually operatable . The voltage divider is configured that a tap voltage being tapped at the divider tap of the voltage divider is manually adj ustable . The voltage divider is implemented e . g . as a potentiometer . In an example , the potentiometer is a three-terminal resistor with a sliding or rotating contact providing the divider tap . The potentiometer forms an adj ustable voltage divider .

[0017] In an embodiment , the test circuit comprises a voltage adapter resistor which couples the first terminal of the voltage divider to the supply terminal . Advantageously, in every possible position of the potentiometer, the tap voltage has a lower value than the supply voltage provided at the supply terminal . Even in case of a high value of the supply voltage , the tap voltage has a value that is appropriate for further measurement . For example , the supply voltage has a value of 30 V and the resistance of the voltage adapter resistor is twice the resistance of the voltage divider ; then the tap voltage has a value between 0 V and 10 V .

[0018] In an embodiment of the test circuit , the analog terminal is designed to alternatively provide a digital signal or an analog signal . The analog signal is an analog voltage . The digital signal can be a high or a low voltage ( corresponding to a logical value " 1" or a logical value " 0" ) . Alternatively, the analog signal is an analog current which will be converted to an analog voltage by means of a resistor .

[0019] In an embodiment of the test circuit , the switch of the first number N of switches is coupled to a node between the support resistor and the supply terminal .

[0020] In an embodiment of the test circuit , the first terminal of the voltage divider is coupled to the node between the support resistor and the supply terminal .

[0021] In an alternative embodiment of the test circuit , the switch of the first number N of switches is coupled to a node between the supply input terminal and the support resistor .

[0022] In an alternative embodiment of the test circuit , the first terminal of the voltage divider is coupled to the node between the supply input terminal and the support resistor .

[0023] In an embodiment of the test circuit , the test circuit is free from any active component , such as a transistor, a relay, or an integrated circuit . The test circuit is free from any semiconductor device .

[0024] In an example , the test circuit can be named simulator or input simulator . The test circuit simulates an environment of the industrial device . The test circuit provides an input stimulation for the industrial device . The test circuit is able to create ( real ) signals to attach to the inputs or terminals of a ( real ) industrial device . The test circuit is reali zed as a hardware simulator of an environment of the industrial device . The industrial device is configured such that the test circuit can be attached to the industrial device and that the test circuit can be used for tests of the industrial device .

[0025] In an embodiment , an industrial device comprises a supply line , a reference potential line , a control circuit , a second number M of device terminals and a presence detector . The presence detector is coupled to the supply line , the reference potential line and the control circuit .

[0026] In an embodiment of the industrial device , the presence detector is configured to determine or detect

[0027] - a first value of the supply voltage at the supply line when the presence detector is in a high resistive state , and

[0028] - a second value of the supply voltage when the presence detector is not in a high resistive state .

[0029] In an embodiment , the industrial device comprises a threshold adapter . The threshold adapter comprises a second number M of device voltage dividers . A first terminal of a device voltage divider of the second number M of device voltage dividers is coupled to a device terminal of the second number M of device terminals . A second terminal of the device voltage divider of the second number M of device voltage dividers is coupled to the reference potential line . A divider tap of the device voltage divider of the second number M of device voltage dividers is coupled to the control circuit .

[0030] In an embodiment of the industrial device , the control circuit comprises an analog-to-digital converter . The divider tap of the device voltage divider of the second number M of device voltage dividers is coupled or connected to an input of the analog-to-digital converter .

[0031] In an embodiment of the industrial device , the control circuit is reali zed as microcontroller or microprocessor .

[0032] In an embodiment of the industrial device , the second number M is equal to the first number N . Alternatively, the second number M is less than the first number N . Alternatively, the second number M is larger than the first number N ( in this case there are some terminals of the industrial device which cannot be tested by means of the test circuit ) .

[0033] In an embodiment of the industrial device , the threshold adapter comprises a second number M of comparators and a reference voltage divider with a first terminal , a second terminal and a divider tap . The divider tap of the device voltage divider of the second number M of device voltage dividers is coupled to a first input of a comparator of the second number M of comparators . An output of the comparator of the second number of comparators is coupled to a terminal of the control circuit . The first terminal of the reference voltage divider is coupled e . g . to the supply line , a further supply line or an output of a supply circuit of the industrial device . The second terminal of the reference voltage divider is coupled to the reference potential line . The divider tap of the reference voltage divider is coupled to a second input of the comparator of the second number M of comparators .

[0034] In an embodiment , the threshold adapter further comprises a reference resistor and a reference transistor . The reference transistor and the reference resistor form a series circuit . The series circuit is coupled to the second input of the comparator of the second number M of comparators and to the reference potential line .

[0035] In an embodiment , the industrial device further comprises a first diode and a voltage terminal . The voltage terminal is coupled to the supply line via the first diode . The voltage terminal is e . g . a voltage terminal of a universal serial bus , abbreviated USB .

[0036] In an embodiment of the industrial device , the first and the second value of the supply voltage which are detected by the presence detector are measured by the control circuit . In case the first value and the second value are approximately equal , the test circuit is not connected to the industrial device . In case the first value is signi ficantly higher than the second value , the test circuit is connected to the industrial device . Thus , in case of the test circuit being connected to the industrial device , the first value VI and the second value V2 follow the equation :

[0037] VI > V2 + const , wherein const is a constant such as e . g . 0 . 5 V or 1 V . in case of the test circuit being not connected to the industrial device , the first value VI and the second value V2 follow the equation :

[0038] VI < V2 + const , wherein const has the same value as in the equation above . The control circuit performs the calculation and generates a signal or sets a flag indicating the presence or the absence of the test circuit at the industrial device . In case of presence the control circuit operates in a simulation mode . The simulation mode can be named test mode . In case of absence the control circuit operates in a normal operation or in a normal operation mode .

[0039] In an embodiment of the industrial device , the presence detector comprises

[0040] - a detector voltage divider with a first terminal coupled to the supply line , a second terminal coupled to the reference potential line and a divider tap coupled to the control circuit , and

[0041] - a series circuit of a detector resistor and a detector transistor .

[0042] The series circuit is coupled to the supply line and to the reference potential line . The control circuit is coupled to a control terminal of the detector transistor .

[0043] In an embodiment , the industrial device comprises a device out of a group consisting of a display device , sensor interface , data logger and a controller . In an embodiment , an arrangement comprises a test circuit and an industrial device . The test circuit is coupled or connected to the industrial device .

[0044] In an embodiment of the arrangement , the supply terminal is connected to the supply line . The reference potential terminal is connected to the reference potential line . At least one of the first number of digital terminals is connected to at least one of the second number M of device terminals .

[0045] In an example , M < N . Thus , each device terminal of the second number M of device terminals is connected to a corresponding digital terminal of the first number of digital terminals . Thus , the test circuit is able to provide signals to all of the exiting device terminals of the industrial device . In case of M < N, there are N-M digital terminals of the first number of digital terminals which are not used in an embodiment of the arrangement .

[0046] In an alternative example , M > N . Thus , some device terminals are not tested by the test circuit .

[0047] In an embodiment of the arrangement , the test circuit and the industrial device are reali zed as two separate parts . The test circuit and the industrial device are fabricated as two separate parts .

[0048] The test circuit described above is particularly suitable for the industrial device and for the arrangement . Features described in connection with the test circuit can therefore be used for the industrial device and for the arrangement and vice versa . In an embodiment of the arrangement , the test circuit is configured as input test circuit for the industrial device . The industrial device has an USB interface .

[0049] In an embodiment of the arrangement , the industrial device is a small industrial device or a small intelligent device . The industrial device is powered e . g . with 24VDC, for extended use alternatively with 12VDC to 24VDC . Such industrial devices may also have digital and analog inputs to support di f ferent functionalities .

[0050] In an embodiment of the arrangement , the industrial device has a possibly low-cost but fast enough connection to a PC or notebook for data trans fer (program, configuration etc . ) . Since today many control circuits such as microcontrollers contain an USB interface including the USB-PHY, this would be an advantageous connection . Moreover, a USB device can be powered from the USB bus which would allow to perform development and commissioning even i f the device supply voltage of 12 / 24V is not connected ( dual supply) .

[0051] In an embodiment of the arrangement , to achieve a low-cost solution, a non-isolated USB interface is used for example . An isolated interface is also possible , but its costs are considerably higher ( an USB isolator like ISOUSB111 from Texas Instruments and an isolated DC-DC converter for power from the USB bus ) .

[0052] In an embodiment of the arrangement , the industrial device can thus be powered from an external 12 / 24V power supply or from the USB, both being possibly connected at the same time . In an embodiment of the arrangement , it is very helpful to provide to the customer a "test circuit" for such devices containing digital inputs or digital and analog inputs . The test circuit is an auxiliary device which can be connected to the input and power terminals , containing switches for the digital inputs and potentiometers for analog inputs and allows the customer to easily simulate the related functionality "on the table" , before installing the industrial device in the final application .

[0053] In an example , the industrial device provides six digital inputs (named device terminals ) and two analog inputs (named analog device terminals ) . The analog inputs can optionally be used as digital inputs . A typical voltage at the analog input is between OV and 10V . The test circuit has e . g . six switch buttons to simulate the digital terminals and two potentiometers , including the corresponding electric circuits to generate the about 10V voltage to simulate two of the analog terminals . Since the test circuit is free of active components for the analog circuitry ( transistors , Zener diodes ) , the test circuit must not conform in the EU ( and UK correspondingly) to the EMCD (Electromagnetic Compatibility Directive ) . The analog terminal can be used as digital terminal . This can be achieved by turning the potentiometer to one end position or to the other end position thus generating digital values "1" or " 0" .

[0054] In an example , additionally, a small industrial device may support as well analog inputs configurable as voltage or current inputs , which in principle are more di f ficult to simulate , especially without corresponding electronic circuits (voltage to current conversion) . In an example , the task is to implement an input test circuit allowing the user to simulate the digital inputs and the analog voltage or current inputs of the user' s application in order to test the functionality before the industrial device is mounted in the real appliance , the power supply used for simulation being possibly an external 24V or 12V voltage source , or the internal 5V voltage from the USB interface to a PC or notebook . In an example , simulation has the meaning of testing the industrial device , especially the meaning of testing the inputs of the industrial device . Further, the costs shall be minimi zed, and the test circuit shall contain only passive components ( such as resistors and capacitors ) in order to be excluded from the EMCD (which simpli fies the conformity declaration and tests ) .

[0055] In an example , a first challenge are the digital inputs . As they are designed to be compatible with the 24V or 12V supply voltage by setting the reference voltage of the input comparators ( or the 1 / 0 compare threshold i f analog acquired) to about 6 . 5V to fit both supply domains , the USB 5V voltage is too low to comply with this threshold . The conventional solution would be to convert the 5V to 12V or 24V by a step- up converter which would be quite expensive for a small device and thus inappropriate to be implemented inside the device itsel f and, i f implemented in the test circuit , would fail the goal of using only passive components .

[0056] In an example , a second challenge are the analog inputs . I f active circuits are to be avoided, so only simple potentiometers should be used for analog simulation, it would be quite complicated to support 24V or 12V supplies by using for instance microswitches to change between di f ferent resistor values . Even i f for simulation an exact input range of the signal must not necessarily be supported ( the user j ust wants to evaluate the functionality and not the accuracy of the analog inputs ) the usual range of the supply voltage of for instance - 15% to +20% would yield a very inaccurate analog voltage range without the use of active circuits . More di f ficult would be to generate current signals of 0 to 20mA and switch these to the device inputs , which would require a lot of setting switches , probably additional potentiometers and would generate considerable power dissipation . Furthermore , simulating analog 0 to 10V inputs from 5V USB would be impossible without active circuits . In an example , the test circuit may ful fill these challenges .

[0057] In an example , low-cost means are provided within the industrial device corresponding to support di f ferent configurations , which finally leads to the third challenge , how to inform the industrial device about the presence of a test circuit requiring di f ferent handling as normal inputs in the application, without having to spend for instance an additional terminal for a detection signal .

[0058] In an example , the test circuit and the industrial device have one or more than one of the following features :

[0059] - the input test circuit is built without active components , only passive components . In this way it can be excluded from the EU EMC Directive which saves costs ( testing) and simpli fies the CE conformity declaration,

[0060] - an extended range of the supply voltage due to the possibility to power the industrial device ( and the test circuit ) from 5V USB, in this case one cannot generate for instance 10V analog signals without active components , even for digital inputs is the voltage too low, - adaption of the digital input threshold according to the supply voltage ( 12V or 24V from an external power supply or 5V from the internal USB interface ) ,

[0061] - adaption of the analog input measurement range according to the supply voltage ,

[0062] - reconfiguration for simulation of analog current inputs to voltage which can be generated with passive components ,

[0063] - detection of the presence of the test circuit in order to change these setting accordingly (which are di f ferent from a normal operation of the industrial device ) .

[0064] In an example , in fact , the circuits are mostly in the industrial device itsel f . The test circuit is built due to this very simply and contains only an additional detection resistor .

[0065] The following description of figures of embodiments shall further illustrate and explain aspects of the test circuit , the industrial device and the arrangement . Parts and components with the same structure and the same ef fect , respectively, appear with equivalent reference symbols . Insofar as parts and components correspond to one another in terms of their function in di f ferent figures , the description thereof is not repeated for each of the following figures .

[0066] Figures 1A to 1C show examples of an arrangement comprising a test circuit and an industrial device ;

[0067] Figures 2A and 2B show examples of details of an arrangement comprising a test circuit and an industrial device ; and Figures 3A and 3B show an example of a measurement set up and of measurement signals of an arrangement comprising a test circuit and an industrial device .

[0068] Figure 1A shows an example of an arrangement 10 comprising a test circuit 11 and an industrial device 50 . The test circuit 11 comprises a supply terminal 12 , a reference potential terminal 13 , a first number N of digital terminals 14 , and a first number N of switches 17 . A switch 17 of the first number N of switches 17 couples or connects the supply terminal 12 to a digital terminal 14 of the first number N of digital terminals 14 . In Figure 1A, the first number N is 1 . Alternatively, as indicated by the dots , the first number N is at least two , three , four, five or six .

[0069] Each switch of the first number N of switches 17 is implemented as a manually operated electromechanical device . The on and of f position of the switches is set by hand . A switch 17 of the first number N of switches 17 is implemented e . g . as one of a toggle switch, a rotary switch, a pushbutton switch, a DIP switch, and a rocker switch .

[0070] Furthermore , the test circuit 11 comprises a voltage divider 21 with a first terminal 22 , a second terminal 23 and a divider tap 24 . The first terminal 22 of the voltage divider 21 is coupled or connected to the supply terminal 12 . The second terminal 23 of the voltage divider 21 is coupled or connected to the reference potential terminal 13 . The divider tap 24 of the voltage divider 21 is coupled to an analog terminal 26 of the test circuit 11 . The analog terminal 26 can also be named analog / digital terminal 26 . As indicated with dots in Figure 1A, the test circuit 11 optionally comprises at least a further analog terminal and at least a further voltage divider which are implemented such as the analog terminal 26 and the voltage divider 21 .

[0071] The voltage divider 21 provides a tap voltage UAN at the divider tap 24 . The voltage divider 21 is configured that the tap voltage UAN is manually adj ustable . The voltage divider 21 is a resistive voltage divider . The position of the voltage divider tap 24 is set by hand .

[0072] Additionally, the test circuit 11 comprises a supply input terminal 35 and a support circuit 36 . The supply input terminal 35 is coupled to the supply terminal 12 via the support circuit 36 . The switch 17 of the first number N of switches 17 is coupled or connected to a node between the support circuit 36 and the supply terminal 12 . Moreover, the first terminal 22 of the voltage divider 21 is coupled or connected to the node between the support circuit 36 and the supply terminal 12 .

[0073] The supply input 35 and the reference potential terminal 13 are configured such that a voltage source ( such as e . g . a battery, a mains adapter or a voltage generator ) can be connected to the supply input 35 and the reference potential terminal 13 .

[0074] The test circuit 11 only comprises passive components . The test circuit 11 is free of active components such as transistors or integrated circuits .

[0075] The industrial device 50 comprises a supply line 51 , a reference potential line 73 , a control circuit 52 , and a second number M of device terminals 53 . The control circuit 52 is reali zed as microcontroller or microprocessor . The control circuit 52 can be named control unit .

[0076] The industrial device 50 comprises an USB interface 68 . The industrial device 50 further comprises a first diode 81 and a voltage terminal 82 . The voltage terminal 82 is coupled to the supply line 51 via the first diode 81 . The voltage terminal 82 is connected or coupled to a supply terminal of the USB interface 68 .

[0077] The industrial device 50 further comprises a presence detector 83 coupled to the supply line 51 . The presence detector 83 is coupled to the reference potential line 73 . The presence detector 83 is connected to the control circuit 52 . The presence detector 83 is configured to determine a first value of a supply voltage US 1 at the supply line 51 when the presence detector 83 is in a high resistive state , and a second value of the supply voltage US 1 when the presence detector 83 is not in a high resistive state .

[0078] The industrial device 50 further comprises a supply circuit 89 which is connected to the supply line 51 . An output of the supply circuit 89 is connected to the control circuit 52 . Optionally, the supply circuit 89 is connected to the voltage terminal 82 .

[0079] The industrial device 50 further comprises a threshold adapter 90 connected to a device terminal 53 of the second number M of device terminals 53 . The threshold adapter 90 is connected to the control circuit 52 . The threshold adapter 90 is connected to the output of the supply circuit 89 . Optionally (as shown in Figure 2B) , the threshold adapter 90 is connected to the reference potential line 73.

[0080] The industrial device 50 comprises an analog device terminal 62. The analog device terminal 62 is coupled or connected to the control circuit 52. In the arrangement 10, the test circuit 11 is coupled or connected to the industrial device 50. For example, the supply terminal 12 is connected to the supply line 51. The reference potential terminal 13 is connected to the reference potential line 73. At least one of the first number of digital terminals 14 is connected to at least one of the second number M of device terminals 53. The analog terminal 26 is coupled or connected to the analog device terminal 62. The analog device terminal 62 is connected or coupled to the control circuit 52 (e.g. as shown in Figure 1C, to an analog-to-digital converter of the control circuit 52) .

[0081] The voltage terminal 82 provides a voltage with a value of e.g. 5 V. The voltage is provided e.g. by an USB interface 68. At the reference potential line 73 and at the reference potential terminal a reference potential GND is tapped. The reference potential GND equals 0 V.

[0082] In an alternative, not-shown embodiment, the switch 17 of the first number N of switches 17 is coupled to a node between the supply input terminal 35 and the support circuit 36.

[0083] In an alternative, not-shown embodiment, the first terminal 22 of the voltage divider 21 is coupled to the node between the supply input terminal 35 and the support circuit 36. Figure IB shows an example of an arrangement 10 comprising a test circuit 11 and an industrial device 50 which is a further development of the embodiments shown in Figure 1A. In Figure IB, the first number N and the second number M are three . Thus , the test circuit 11 comprises the first number N of digital terminals 14 to 16 and the first number N of switches 17 to 19 . The industrial device 50 comprises the second number M of device terminals 53 to 55 . The digital terminals 14 to 16 are directly connected to the device terminals 53 to 55 .

[0084] Furthermore , the test circuit 11 comprises a further voltage divider 21 ' which is reali zed such as the voltage divider 21 . A divider tap 24 ' of the further voltage divider 21 ' is coupled or connected to a further analog terminal 27 of the test circuit 11 . The industrial device 50 comprises a further analog device terminal 63 . The further analog device terminal 63 is connected to the further analog terminal 27 of the test circuit 11 . The further analog device terminal 63 is coupled or connected to the control circuit 52 .

[0085] In an example , the second number M is 8 and the industrial device 50 is free of any analog device terminal . In an alternative example , the second number M is 6 and the industrial device 50 comprises the analog device terminal 53 and the further analog device terminal 63 .

[0086] In an alternative , not shown embodiment , indicated by dots , the test circuit 11 comprises at least another voltage divider which is reali zed such as the voltage divider 21 . A divider tap of the at least another voltage divider is coupled to at least another analog terminal of the test circuit 11 . The industrial device 50 comprises at least another analog device terminal . The at least another analog device terminal is connected to the at least another analog terminal of the test circuit 11 and to the control circuit 52 .

[0087] Figure 1C shows an example of an arrangement 10 comprising a test circuit 11 and an industrial device 50 which is a further development of the embodiments shown above . The support circuit 36 comprises a support resistor 37 which is coupled or connected to the supply input terminal 35 and to the supply terminal 12 . The test circuit 11 comprises a voltage adapter resistor 25 . The first terminal 22 of the voltage divider 21 is coupled or connected to the node between the support circuit 36 and the supply terminal 12 via the voltage adapter resistor 25 .

[0088] The presence detector 83 comprises a detector voltage divider 85 with a first terminal 86 coupled to the supply line 51 , a second terminal 87 coupled to the reference potential line 73 and a divider tap 88 coupled to the control circuit 52 . An analog voltage USM is tapped at the divider tap 88 of the detector voltage divider 85 . The presence detector 83 comprises a series circuit 103 of a detector resistor 104 and a detector transistor 105 . The series circuit 103 couples the supply line 51 to the reference potential line 73 . The control circuit 52 is coupled to a control terminal of the detector transistor 105 .

[0089] The industrial device 50 comprises a second diode 91 and a capacitor 92 . The capacitor 92 is reali zed as smoothing capacitor . An anode of the second diode 91 is connected to the supply line 51 . A cathode of the second diode 91 is connected to a first electrode of the capacitor 92 . At the capacitor 92, an internal voltage US2 is tapped. The internal voltage US2 is tapped at the cathode of the second diode 91. The supply circuit 89 comprises a voltage converter 95 with an input coupled to the second diode 91. The internal voltage US2 is applied to the input of the voltage converter 95. The supply circuit 89 comprises a third diode 93. An output of the voltage converter 95 is coupled or connected to the third diode 93, e.g. to an anode of the third diode 93. The voltage converter 95 is implemented as e.g. switching converter or DC / DC converter. The voltage converter 95 generates a voltage of about the same value - e.g. 5V - as provided at the USB voltage terminal 82.

[0090] The supply circuit 89 comprises a regulator 97. The output of the voltage converter 95 is coupled via the third diode 93 to an input of the regulator 97. At an output of the regulator 97 a regulated supply voltage US3 is provided, e.g. 3.3V of the control circuit (and further electronic circuits) . The regulator 97 is e.g. a low-dropout regulator. A cathode of the third diode 93 is connected to the input of the regulator 97. The control circuit 52 is connected to the output of the regulator 97.

[0091] The supply circuit 89 comprises a fourth diode 96. The voltage terminal 82 is coupled via the fourth diode 96 to the input of the regulator 97. A cathode the fourth diode 96 is connected to the input of the regulator 97. The regulator 97 (and so the electronic circuits) can thus be powered either from the supply terminal 12 or from the internal voltage 82 from the USB interface (dual supply) . The internal supply voltage of the regulator 97, a little lower than 5V due to the voltage drop over the third diode 93 or the fourth diode 96 can be further used for other purposes (for which the about 3 . 3V supply voltage of the electronic circuits may be too low) , for instance in case of a display to power the backlight driver .

[0092] The control circuit 52 includes an analog-to-digital converter 64 , abbreviated ADC . The device terminal 53 of the second number M of device terminals 53 - 55 is coupled via a second number M of device voltage dividers 56 ( as shown in Figure 1C ) to an input of the ADC 64 ( in this example , the comparator 65 is not used) . Alternatively, the second number M of device terminals 53 - 55 is coupled via the threshold adapter 90 to a digital input of the control circuit 52 , wherein the threshold adapter 90 comprises the second number M of device voltage dividers 56 and a second number M of comparators 65 - 67 ( as illustrated in Figure 2B ) . An input signal UIN is provided at the device terminal 53 . The input signal UIN is digiti zed by the comparator 65 . Thus , it is possible but not required to provide an ADC of the control circuit 52 for determination of the input signal UIN .

[0093] The analog device terminal 62 is coupled to an input of a further ADC 64 ' of the control circuit 52 . For example , the industrial device 50 comprises an additional voltage divider 74 which couples the analog device terminal 62 to the reference potential line 73 . A divider tap of the additional voltage divider 74 is coupled or connected to the input of the further ADC 64 ' of the control circuit 52 . The additional voltage divider 74 includes two resistors which are connected in series . The divider tap is located between the two resistors . The divider tap 88 of the detector voltage divider 85 is coupled or connected to an input of an additional ADC 64 ' ’ of the control circuit 52 .

[0094] In an example , the second number M is equal to the first number N . Thus , the device terminals 53 - 55 are connected to the digital terminals 14 - 16 . For each of the second number M of device terminals 53 - 55 , there is a corresponding digital terminal of the first number of digital terminals 14 - 16 . Alternatively, the second number M is less than the first number N . In this case , at least one of the digital terminals 17 - 19 is not used . Alternatively, M>N, in this case at least one of the device terminals 53 - 55 will not be tested .

[0095] The control circuit 52 ( e . g . a microcontroller ) identi fies a connected test circuit 11 in order to adapt the settings accordingly for simulation or testing the industrial device 50 or perform normal input acquisition i f no test circuit 11 is connected . This operation takes place at power up . The arrangement 10 does not requires an identi fication signal to signali ze the presence of a test circuit 11 ( thus , an additional terminal or an active circuit in the test circuit 11 for such an identi fication signal is not required) .

[0096] The test circuit 11 can be implemented as shown in Figures 1A to 1C to identi fy a connected test circuit 11 .

[0097] On the test circuit 11 , in series with the supply voltage to the test circuit 11 , the support resistor 37 - e . g . having a low resistance value - is inserted . Its resistance value is chosen that during normal operation only a small voltage drop occurs . The value depends on the normal maximum current drawn by the industrial device 50 . For small industrial devices 50 some 100mA to 200mA can be considered . In such a case , even a 10Q resistor for instance would cause a maximum voltage-drop of 2V, which even at 12V supply is acceptable . The resistance value can of course be adj usted according to the speci fic current consumption of the industrial device 50 . The support resistor 37 has a resistance value RS in a range between 1 Q and 20 Q or between 5 Q and 15 Q .

[0098] Inside the industrial device 50 , the detector resistor 104 is a further low resistance resistor . The detector resistor 104 is connected between the supply line 51 (having the supply voltage US 1 ) and the reference potential line 73 (having 0V) by means of the detector transistor 105 . The detector transistor 105 is e . g . a metal-oxide-semiconductor fieldef fect transistor, abbreviated MOSFET or a bipolar transistor . The resistance value of the detector resistor 104 shall be chosen that , when connected, a distinct measurable voltage drop of the supply voltage US 1 at the supply line 51 occurs . This can be measured with the detector voltage divider 85 which generates the analog voltage USM . For this measurement , the detector transistor 105 is turned on by the control circuit 52 for a short period of time , for instance 1ms . In this way, even i f a relatively high current flows during the measurement , so a higher impulse power dissipation occurs , its mean value is low; thus , no especially high-power resistor and transistor are necessary .

[0099] This measurement by means of the presence detector 83 takes place at power-up . The test circuit 11 cannot be connected or disconnected without turning the device power of f . First the supply voltage US 1 is measured before connecting the detector resistor 104 , then the supply voltage US 1 is measured after connecting the detector resistor 104 and the difference is calculated to decide, if the test circuit 11 is connected to the industrial device 50 or not. If the industrial device 50 is powered only from the voltage terminal 82 - having (about 5V - , this measurement is not necessary, the corresponding settings for simulation can directly be activated. The USB interface 68 provides the 5V. Only if the supply voltage US1 shows the presence of an external power supply with 12V or 24V at the supply terminal 12, the control circuit 52 shall know if a test circuit 11 is connected or not, so that the corresponding settings can be performed.

[0100] To improve the measurement resolution, during power-up the current consumption can be kept low by not turning on yet the main consumer (for instance in case of a display keep the backlight turned off during the measurement) . Thus, the difference in voltage-drop over the support resistor 37 in the test circuit 11 is even better recognizable. Since the presence detector 83 is connected before the second diode 91, the voltage drop is not sensed inside the industrial device 50 as the internal voltage US2 is buffered by the capacitor 92 (necessary for other purposes as well) . The second diode 91 performs a reverse polarity protection. The capacitor 92 is an electrolytic capacitor 92.

[0101] In an alternative, not shown embodiment, the analog device terminal 62 is configured as current input. In this case, a different circuit (not shown in FIG 1C) is switched between the analog device terminal 62 and the input of the further ADC 64' (or an input of another ADC) . The industrial device 50 comprises a current measurement resistor. The current measurement resistor couples the analog device terminal 62 to the reference potential line 73. The input of the further ADC 64' is coupled or connected to the analog device terminal 62. The current measurement resistor has a value R which converts the maximum input current of e.g. 20mA into a voltage equal to a reference voltage VREF of the further ADC 64' : R=VREF / 20mA (for instance if VREF=2.5V, R=2.5V / 20mA=125Q) .

[0102] In an alternative, not shown embodiment, the ADC 64, the further ADC 64' and the additional ADC 64' ’ are realized by a single ADC having an input coupled via a multiplexer to the different taps and terminals 53, 62, 88.

[0103] Figure 2A shows an example of details of an industrial device 50 which is a further development of the embodiments shown above. In principle, since complex circuits and configuration switches in the test circuit 11 are avoided, corresponding appropriate adjustments are done inside the industrial device 50, depending on the actual supply voltage US1 used: 12V, 24V or 5V. The presence of the 5V USB supply voltage can easily be detected by the control circuit 52, e.g. a microcontroller. Nevertheless, this does not guarantee that the supply of the industrial device 50 and of the test circuit 11 is 5V (minus voltage drop on the protection circuits, at least a diode) since the user may connect an external power supply to the test circuit 11 as well.

[0104] Therefore, the supply voltage US1 at the supply line 51 inside the industrial device 50 is first measured to identify the value of the supply voltage US1 used. This can be simply done by a connecting the detector voltage divider 85 (having two resistors 99, 100) to the supply line 51 and applying the analog voltage USM to an input of an analog-to-digital converter, abbreviated ADC, inside the control circuit 52. The measurement accuracy (decreased by the voltage division) is not very important , only the range of the supply voltage US 1 ( 24V, 12V or 5V) has to be detected .

[0105] The ratio between the supply voltage US 1 and the analog voltage USM provided to the control circuit 52 is determined by the two resistors 99 , 100 . This ratio can be appropriately chosen, for instance about 10 : 1 , so that with US 1=3 OV at the input the analog voltage USM to the additional ADC 64 ' ’ is 3V .

[0106] Once the supply voltage US 1 is identi fied, corresponding measures or steps to adapt the input acquisition can be accordingly set . Thus , the detector voltage divider 85 and the additional ADC 64 ' ’ are configured to detect the actual value of the supply voltage US 1 .

[0107] Figure 2B shows an example of details of an industrial device 50 which is a further development of the embodiments shown above . In Figure 2B, the threshold adapter 90 of the industrial device 50 is shown . The threshold adapter 90 comprises a second number M of device voltage dividers 56 - 58 . A first terminal 59 of a device voltage divider 56 of the second number M of device voltage dividers 56 - 58 is coupled or connected to a device terminal 53 of the second number M of device terminals 53 - 55 . A second terminal 60 of the device voltage divider 56 of the second number M of device voltage dividers 56 - 58 is coupled or connected to the reference potential line 73 . A divider tap 61 of the device voltage divider 56 of the second number M of device voltage dividers 56 - 58 is coupled to the control circuit 52 .

[0108] The threshold adapter 90 comprises a second number M of comparators 65 - 67 and a reference voltage divider 69 . The divider tap 61 of the device voltage divider 56 of the second number M of device voltage dividers 56 - 58 is coupled or connected to a first input of a comparator 65 of the second number M of comparators 65 - 67 . An output of the comparator 65 of the second number of comparators 65 - 67 is coupled or connected to an input terminal of the control circuit 52 . The resistor of the device voltage divider 56 between the divider tap 61 and the second terminal 60 achieves that a voltage at the first input of the comparator 65 has the reference potential GND in case the device terminal 53 ( and thus the first terminal 59 ) is left unconnected and thus may be floating . Therefore , the switch 17 can be reali zed as a simple on / of f switch . Alternatively, the switch 17 is reali zed as a change-over switch with a first input connected to the supply terminal 12 and a second input connected to the reference potential terminal 13 .

[0109] A first terminal 70 of the reference voltage divider 69 is coupled or connected to a known voltage , for instance to the output of the supply circuit 89 . A second terminal 71 of the reference voltage divider 69 is coupled or connected to the reference potential line 73 . A divider tap 72 of the reference voltage divider 69 is coupled or connected to a second input of the comparator 65 of the second number M of comparators 65 - 67 .

[0110] The threshold adapter 90 further comprises a reference resistor 75 and a reference transistor 76 . The reference transistor 76 and the reference resistor 75 form a series circuit . The series circuit is coupled or connected on one side to the second input of the comparator 65 of the second number M of comparators 65 - 67 and on the other side to the reference potential line 73 . For the digital inputs , the input circuits are already designed to support 24V or 12V signals . This can be done as for instance by using the comparator 65 and the device voltage divider 56 for the input signal at the device terminal 53 and a reference voltage to set the threshold on the second input of the comparator 65 , this being simply generated for instance by the reference voltage divider 69 from the regulated supply voltage US3 . In this example the input threshold Uthin of about 6 . 5V is defined by the division ratio of the input signal UIN through the device voltage divider 56 with resistors having resistances Rl , R2 and the comparator reference voltage set by the reference voltage divider 69 with resistances R3 , R4 from the regulated supply voltage US3 or VDD ( for instance 3 . 3V) :

[0111] Uthin = (R1 + R2 ) / R2 • R4 / (R3 + R4 ) • US3

[0112] I f the detected supply voltage US 1 at the supply terminal 12 and at the supply line 51 is ( almost ) 5V, so supply from USB, the input threshold can be adapted to an appropriate value ( for instance 2 . 5V) by lowering the reference voltage for the second input of the comparator 65 through the connection of the reference resistor 75 in parallel to a resistor of the reference voltage divider 69 by the reference transistor 76 . The reference transistor 76 is controlled by the control circuit 52 . The reference transistor 76 is e . g . a MOSFET or a bipolar transistor .

[0113] Of course , having more device terminals 53 - 55 requires correspondingly more comparators 65 - 67 , but the reference voltage is generated once for all of them, therefore only one reference resistor 75 and one reference transistor 76 are required for changing the threshold, so the costs are negligible . The device terminals 53 - 55 can be also named digital inputs .

[0114] Alternatively, i f the industrial device 50 requires only slow digital inputs , instead of using the comparator 65 the signal from the device voltage divider 56 can be directly applied to the input of the ADC 64 of the control circuit 52 (being e . g . a microcontroller ) , analog acquired and compared with a corresponding level ( reference value ) to decide i f the signal is 0 or 1 . The reference value can be then directly adj usted in the software ( instead of reference transistor and reference resistor ) in case of 5V USB supply for simulation .

[0115] In both cases corresponding overvoltage / undervoltage protection circuits are implemented (protection diodes not shown in Figure 2B ) .

[0116] For the analog device terminal 62 (which can be named analog input ) or the analog device terminals of the industrial device 50 two steps are performed for simulation : first the generation of real current inputs for simulation would be quite di f ficult . Nevertheless , the user only desires to veri fy his program / conf iguration related to the analog device terminal 62 or terminals , for instance displaying the analog values . At this stage it does not really matter how the analog values are generated ( as in the real application will be ) so that for simulation it is very convenient to always generate voltage signals to the analog device terminal 62 or terminals , even i f current inputs were programmed / conf igured . The control circuit 52 , identi fying the simulation mode by detecting the presence of the test circuit 11 simply reconfigures the analog device terminal 62 or terminals from current to voltage only for the simulation . Thus , the analog signals can always be generated as voltage signals by the test circuit 11 , which is quite easily done by means of a simple potentiometer reali zing the voltage divider 21 or several potentiometers connected to the supply terminal 12 .

[0117] The second step is to adapt the useful analog input voltage range to the actual supply voltage US 1 which can be measured as previously shown at the detection of the supply voltage US 1 . Practically the analog-to-digital converter in the control circuit 52 is configured to measure the expected maximum voltage range at an input which corresponds to the maximum supply voltage ( of 28 . 8V for 24V +20% ) . By measuring the real value of the input voltage , the useful range for simulation can be correspondingly adapted to the applied supply voltage US 1 . This measurement could be done once at power-up, but for better compensation of possible supply voltage variations during simulation it should be done each time before the analog inputs will be acquired . Surely, the lower the supply voltage US 1 , the poorer the resolution will be , i . e . in case of powering only from USB the worst . But not resolution or accuracy are important for simulation but the functionality; the analog values are set anyway very approximately by manually turning the potentiometers .

[0118] Example for adapted settings and resulting resolutions of a 12-bit ADC :

[0119] - Maximum input range : 0 to 28 . 8V results in 28800mV / 4096 = 7mV / bit

[0120] - Supply voltage 24V results in 24000mV / 7mV = 3428 useful bits ( > 11-bit resolution)

[0121] - Supply voltage 12V results in 12000mV / 7mV = 1714 useful bits ( > 10-bit resolution) - Supply voltage 4 . 5V results in 4500mV / 7mV = 642 useful bits ( > 9-bit resolution)

[0122] One can see that even in case of a quite low supply voltage from USB of for example 4 . 5V a resolution of 9-bit is still available , which is enough for simulation which means testing the industrial device 50 .

[0123] Figures 3A and 3B show an example of a measurement set up and of measurement signals of an arrangement 10 comprising a test circuit 11 and an industrial device 50 which is a further development of the embodiments shown above . In this LT Spice simulation example at 12V supply voltage , the support resistor 37 is 10Q, a load resistor 94 is I kQ, so the low consumption at power-up is about 10mA, the test current determined by the detector resistor 104 , here 100Q is about 100mA and the well measurable voltage drop of the supply voltage US 1 is about IV . The internal voltage US2 remains practically unchanged . A voltage source 110 generates the supply voltage US 1 .

[0124] Finally, it should be mentioned that the real circuits such as an example of the industrial device 50 optionally also contains di f ferent further protection components , not shown in this description, like overvoltage , surge , ESD, reverse polarity protection etc .

[0125] The embodiments shown in Figures 1A to 3B as stated represent example embodiments of an arrangement 10 ; therefore , they do not constitute a complete list of all embodiments according to the arrangement 10 . Actual arrangements may vary from the embodiments shown in terms of parts , devices and circuits , for example . List of Reference Numerals

[0126] 10 arrangement

[0127] 11 test circuit

[0128] 12 supply terminal

[0129] 13 reference potential terminal

[0130] 14 - 16 digital terminal

[0131] 17 - 19 switch

[0132] 21 , 21 ' voltage divider

[0133] 22 first terminal

[0134] 23 second terminal

[0135] 24 , 24 ' divider tap

[0136] 25 voltage adapter resistor

[0137] 26 , 27 analog terminal

[0138] 35 supply input terminal

[0139] 36 support circuit

[0140] 37 support resistor

[0141] 50 industrial device

[0142] 51 supply line

[0143] 52 control circuit

[0144] 53 - 55 device terminal

[0145] 56 - 58 device voltage divider

[0146] 59 first terminal

[0147] 60 second terminal

[0148] 61 divider tap

[0149] 62 , 63 analog device terminal

[0150] 64 , 64 ' , 64 ' ’ analog-to-digital converter

[0151] 65 - 67 comparator

[0152] 68 USB interface

[0153] 69 reference voltage divider

[0154] 70 first terminal

[0155] 71 second terminal

[0156] 72 divider tap 73 reference potential line

[0157] 74 additional voltage divider

[0158] 75 reference resistor

[0159] 76 reference transistor

[0160] 81 first diode

[0161] 82 voltage terminal

[0162] 83 presence detector

[0163] 85 detector voltage divider

[0164] 86 first terminal

[0165] 87 second terminal

[0166] 88 divider tap

[0167] 89 supply circuit

[0168] 90 threshold adapter

[0169] 91 second diode

[0170] 92 capacitor

[0171] 93 third diode

[0172] 94 , load resistor

[0173] 95 voltage converter

[0174] 96 fourth diode

[0175] 97 regulator

[0176] 99 , 100 resistor

[0177] 103 series circuit

[0178] 104 detector resistor

[0179] 105 detector transistor

[0180] 110 voltage source

[0181] GND reference potential

[0182] UAN, UAN' tap voltage

[0183] UIN, UIN' input signal

[0184] UIN' ' input signal

[0185] USM analog voltage

[0186] US 1 supply voltage

[0187] US2 internal voltage

[0188] US3 regulated supply voltage

Claims

Claims1. A test circuit (11) , comprising- a supply terminal (12) ,- a reference potential terminal (13) ,- a first number N of digital terminals (14 - 16) ,- a first number N of switches (17 - 19) ,- a supply input terminal (35) , and- a support resistor (37) , wherein the support resistor (37) is coupled to the supply terminal (12) and to the supply input terminal (35) , and wherein a switch (17) of the first number N of switches(17 - 19) couples the supply terminal (12) to a digital terminal (14) of the first number N of digital terminals (14 - 16) .

2. The test circuit (11) of claim 1, wherein a switch (17) of the first number N of switches(17 - 19) is implemented as a manually operated electromechanical device.

3. The test circuit (11) of claim 1 or 2, wherein the test circuit (11) comprises- an analog terminal (26) and- a voltage divider (21) with a first terminal (22) , a second terminal (23) and a divider tap (24) , wherein the first terminal (22) of the voltage divider (21) is coupled to the supply terminal (12) , wherein the second terminal (23) of the voltage divider (21) is coupled to the reference potential terminal (13) , andwherein the divider tap (24) of the voltage divider (21) is coupled to the analog terminal (26) of the test circuit (11) •4. The test circuit (11) of claim 3, wherein the test circuit (11) comprises a voltage adapter resistor (25) which couples the first terminal (22) of the voltage divider (21) to the supply terminal (12) .

5. The test circuit (11) of claim 3 or 4, wherein the voltage divider (21) is configured that a tap voltage (UAN) being tapped at the divider tap (24) of the voltage divider (21) is manually adjustable.

6. The test circuit (11) of one of claims 1 to 5, wherein the switch (17) of the first number N of switches (17 - 19) is coupled to a node between the support resistor (37) and the supply terminal (12) .

7. The test circuit (11) of one of claims 1 to 6, wherein the test circuit (11) is free from any active component .

8. An industrial device (50) , comprising- a supply line (51) ,- a reference potential line (73) ,- a control circuit (52) ,- a second number M of device terminals (53 - 55) , and- a presence detector (83) coupled to the supply line (51) and to the reference potential line (73) and configured to detect- a first value of a supply voltage (US1) at the supply line (51) when the presence detector (83) is in a high resistive state, and- a second value of the supply voltage (US1) when the presence detector (83) is not in a high resistive state.

9. The industrial device (50) of claim 8, wherein the presence detector (83) comprises- a detector voltage divider (85) with a first terminal(86) coupled to the supply line (51) , a second terminal(87) coupled to the reference potential line (73) and a divider tap (88) coupled to the control circuit (52) , and- a series circuit (103) of a detector resistor (104) and a detector transistor (105) , wherein the series circuit (103) is coupled to the supply line (51) and to the reference potential line (73) , and wherein the control circuit (52) is coupled to a control terminal of the detector transistor (105) .

10. The industrial device (50) of claim 8 or 9, wherein the industrial device (50) further comprises a threshold adapter (90) and the threshold adapter (90) comprises a second number M of device voltage dividers (56- 58) , wherein a first terminal (59) of a device voltage divider(56) of the second number M of device voltage dividers (56- 58) is coupled to a device terminal (53) of the second number M of device terminals (53 - 55) , wherein a second terminal (60) of the device voltage divider (56) of the second number M of device voltage dividers (56 - 58) is coupled to the reference potential line ( 73 ) , andwherein a divider tap (61) of the device voltage divider (56) of the second number M of device voltage dividers (56- 58) is coupled to the control circuit (52) .

11. The industrial device (50) of claim 10, wherein the control circuit (52) comprises an analog-to- digital converter (64) , and wherein the divider tap (61) of the device voltage divider (56) of the second number M of device voltage dividers (56- 58) is coupled to an input of the analog-to-digital converter ( 64 ) .

12. The industrial device (50) of claim 10, wherein the threshold adapter (90) comprises:- a second number M of comparators (65 - 67) , and- a reference voltage divider (69) , wherein the divider tap (61) of the device voltage divider (56) of the second number M of device voltage dividers (56- 58) is coupled to a first input of a comparator (65) of the second number M of comparators (65 - 67) , wherein an output of the comparator (65) of the second number of comparators (65 - 67) is coupled to a terminal of the control circuit (52) , wherein a first terminal (70) of the reference voltage divider (69) is coupled to an output of a supply circuit (89) of the industrial device (10) , wherein a second terminal (71) of the reference voltage divider (69) is coupled to the reference potential line (73) , and wherein a divider tap (72) of the reference voltage divider (69) is coupled to a second input of the comparator (65) of the second number M of comparators (6567) .

13. The industrial device (50) of claim 12, wherein the threshold adapter (90) further comprises:- a reference resistor (75) and- a reference transistor (76) , wherein the reference transistor (76) and the reference resistor (75) form a series circuit, wherein the series circuit is coupled to the second input of the comparator (65) of the second number M of comparators (65 - 67) and to the reference potential line (73) .

14. The industrial device (50) of any one of claims 8 to 13, wherein the industrial device (50) further comprises:- a first diode (81) , and- a voltage terminal (82) , wherein the voltage terminal (82) is coupled to the supply line (51) via the first diode (81) .

15. An arrangement (10) , comprising- the test circuit (11) of any one of claims 1 to 7, and- the industrial device (50) of any one of claims 8 to 14, wherein the supply terminal (12) is connected to the supply line (51) , wherein the reference potential terminal (13) is connected to the reference potential line (73) , and wherein at least one of the first number of digital terminals (14 - 16) is connected to at least one of the second number M of device terminals (53 - 55) .

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