DIGITALLY ADDRESSABLE ELECTRONIC DEVICE

Abstract: In a system comprising a plurality of digitally addressable electronic devices (11 to 14), all devices have the same con­ struction and are designed for being connected in series to a common centre monitoring station (10). The addressing of these devices is accomplished by means of a plurality of address lines (A,B) which are connected to input means (23) of the respective device. Within each device, a selection gate (31) is connected to the input means which provides an enabling signal if the signal on said address lines has a predetermined bit pattern. Each device further comprises output means (24) connected to said input means (23), to which output means (24) the input means (23) of a next device may be connected. The address lines are connected from the input means (23) to the output means of the device in such a way that the contacts are interchanged and an inverter (25) is inserted in one of said lines. Thereby, the bit pattern forming the address provided at the output is different from the bit pattern received at the input. Thus, along the suit of series connected devices a plurality of different bit patterns is produced so that the position of the correct bit pattern to which the device selection means (31) responds, may be shifted along the series connected devices in order to address the device which is in a predetermined position. Further, the devices may form racks or cabinets including a plurality of modules (15). A preferred application of such devices is in medical surveillance systems in which a plurality of racks or cabinets may be connected serially together and to a centre monitoring station (10), each rack or cabinet being allocated to a different task and including the units which are needed to monitor the vital functions of a patient.

Description: The invention relates to a digitally addressable electronic device in accordance with the prior art portion of claim 1. Digitally addressable electronic devices are generally connected to a bus system in parallel and include gate means which respond to an address in form of a specific bit pattern which is transmitted via address lines included in said bus. In such a system it is necessary to individually set the gate means included in such an addressable device to a specific address. In a system, which includes a plurality of different, addressable devices which may be repeatedly exchanged, this kind of addressing is cumbersome and may lead to trouble which is caused by errors in setting the gate means. Such trouble may become very serious when the digitally addressable electronic devices are medical apparatusses used for monitoring body functions of seriously sick persons so that a failure in monitoring may have lethal consequences. Typically, digitally addressable electronic devices of the above-mentioned kind are used in a larger system comprising a central unit an a plurality of such devices. The erroneous addressing of a device which is not or not properly connected may cause serious problems especially when using the devices in medical systems for monitoring body functions and the like. Usually, each of said devices or boards comprise a plurality of modules which may have the form of plug-in sensor units including a sensor for monitoring a specific body function. Here again, the erroneous addressing of a module which is not or not properly connected to the devices may lead to lethal consequences when using the system in the field of medical care. NEW ELECTRONICS, vol. 18, no. 2, 22nd January 1985, page 29, London, Great Britain, J. A. Pike: "Simplest board encoding" discloses an encoding system for encoding identical boards or digitally adressable electronic devices by their position using a two-line address bus. This prior art encoding system requires a single inverter only for each of said boards or addressable electronic devices which is connected between the input of a first address line and the output of a second one, whilst the second address input is directly connected to the first address output of the board or addressable electronic device. Thus, two-bit address codes depending upon both the address code applied to the input of the first board and the position of the board in question is generated. Thus, the respective address codes applied to the inputs of the respective boards are altered. Thus, the address decoding circuit of each board can be identical. EP-A-0 162 651 discloses a further encoding system for addressing a plurality of serially connected boards depending on their physical position without the need for setting any switches. In each addressable electronic device the respective lines of the address bus are transposed by one position to thereby shifting the bits of the address towards the MSB whilst introducing a "0" for the LSB. US-A-4 015 244 discloses a selective addressing system establishing a self-address code in each addressable electronic device by twisting the address lines and implementing one bit by means of an inverter. IMB TECHNICAL DISCLOSURE BULLETIN, vol. 22, no. 10, March 1980, page 4615, New York, US; S. Meguro "Automatic module detection" discloses a system for detecting the presence or absence of a module on a card. For detecting the presence of the module on a socket a module itself is used as a jumper to signal its insertion. In view of the above prior art, its is an object of the invention to provide a digitally addressable electronic device of the above-mentioned type which is addressable independently of any setting of address registers, gates and the like and which establishes a warning signal if a unit, e.g. a device or a module, is addressed, which is not or not properly connected. This object is met by a digitally addressable electronic device in accordance with the prior art portion of claim 1 having the features indicated in the characterizing portion thereof. In accordance with the present invention, first switch means are provided for directly returning a signal received on the transmitting line to the receiving line upon detection of the missing of an addressed module. The immediate return of the transmitted signal can be readily detected by a central monitoring station controlling the respective addressable electronic devices. In a preferred embodiment of the invention, second switch means are provided for directly returning a signal received on the transmitting line to the receiving line upon the detection of the missing of a further addressed device. In a preferred embodiment of the invention, third switch means are connected to the respective second contacts of the input means and output means for establishing a connection therebetween in response to the control signal being an disenabling signal. Thus, the transmitted signal is blocked within the respective addressed device and not passed to the output connection thereof. In accordance with a further preferred embodiment of the invention, the device comprises input means having a first plurality of N contacts and output means having a second plurality of N contacts, N being an integer. Each contact bears a designation n, n being an integer defined as 1 < n < N. Each n th contact of the first plurality of contacts is directly connected to the (n+1) th contact of the second plurality with the exception of the N th contact of the first plurality which is connected to the 1 st contact of the second plurality via an inverter. The number of addresses which may be defined in this way is 2N. Thus, in the simplest case of only two address lines, four devices may be addressed. In a preferred embodiment of the invention, the device selection means generates the enable signal if all bits of the address signal applied to its input have the same value. Thus, the addressing of the device can be detected by an AND-gate. Further preferred embodiments are defined in the respective subclaims. A preferred application of the invention in the field of medical care wherein devices according to the invention may be designed in form of a cabinet or a rack which may be allocated to a single patient and which receives the specific modules which are needed to supervise the body functions of this patient, as for example the heart activity, breathing rate, brain activity and so on. Such racks or cabinets may be connected in series to a central monitoring station from where the plurality of patients may be supervised. The invention and details thereof which are defined by the subclaims, are more closely described with reference to the embodiments shown in the accompanying drawing, in which Fig.1 is a schematic representation of a patient monitoring system comprising devices according to the invention, Fig. 2 is the circuit diagram of a device used in the system shown in Fig. 1, Fig. 3 is a schematic presentation of the rack addressing scheme used in the system shown in Fig. 1, and Fig. 4 is a schematic representation of a rack addressing system comprising four address lines. Fig. 1 illustrates a patient monitoring system comprised of a centre monitoring station 10 to which four racks 11, 12, 13 and 14 are connected. Each of said racks includes up to eight patient modules 15, one of which is separately shown as a box 16 below the first rack 11. The patient module 16 may include appropriate means to supervise special body functions, as for example pulse frequency, blood pressure, temperature, breathing rate etc., as e.g. a sensor 17 which is connected to the patient module 16 by means of a cable. The racks are serially inter­ connected and the first rack 11 is connected to the centre monitoring station 10 by means of a cable 18. The centre monitoring station includes control means in form of a central processing unit 19 to which the racks 11 to 14 are connected via front end interface 20, whereas to the CPU of the centre monitoring station a display unit 21 is connected via display interface 22. Each of the racks 11 to 14 is assigned to a different task. In order to gather the information produced by the different patient modules 15, these modules are successively addressed and sensed so that the corresponding data are successively received in the centre monitoring station, where the sensed information is processed for being displayed on display unit 21. In order to address the plurality of racks, the cable 18 connecting the first rack 11 to the centre monitoring station 10 as well as the cables connecting serially the different racks 11 to 14 include a plurality of address lines as well as transmitting and receiving lines, the transmitting line T being used to send signals from the centre monitoring station 10 to the addressed patient module whereas the receiving line is used to transmit signals from said patient modules to the centre monitoring station. As shown in the circuit diagram of Fig. 2, the cable 18 connecting the first rack 11 to the centre monitoring station includes seven lines, i.e. a first plurality of two address lines A and B, a second plurality of three address lines C, D and E, a transmitting line T and a receiving line R. Each rack has input means 23, for example in form of an appropriate plug and socket connection. A similar connection forms output means 24 allowing the connection of rack 1 via a cable 18′ to the next serially connected rack 12. In the device of Fig. 2, to address lines A, B a NAND-Gate 31 is connected which produces at its output line 32 an enabling signal if the signals on address lines A, B connected to its inputs are both a logic 1. Only if the module selection unit 33 receives the said enabling signal, it produces at one of its output lines an enabling signal for the associated module 15. The addressed module is determined by the signal present on address lines C, D and E which is connected to the inputs of said module selection unit 33. In the system shown in Fig. 1, all racks 11 to 14 are similar. Thus, each rack is addressed if the signal on address lines A and B connected to the input connection 23 has the bit pattern 1,1. Nevertheless, a selection can be made since the address signal is modified when passing through the device because of the address line B at input connection 23 being connected to the contact A′ of the output connection 24, whereas the address line A at input connection 23 is connected to contact B′ at the output connection 24 via an inverter 25. The result of this measure is that the bit pattern which forms the rack address provided at the output connection 24 is different from the bit pattern fed to the input connection 23. This is shown in more detail in Fig. 3. If at the input connection of rack 1 the bit pattern 0,0 is present, the crossing of the lines and the insertion of the inverter 25 produces at contacts A′, B′ of the output connection the bit pattern 0,1 which is concurrently the bit pattern at the input connection of rack 2 to which said rack responds. Similarly, the bit pattern 0,1 at the input of rack 2 is trans­ formed into the bit pattern 1,1 at the output of this rack. Thus, at the input of rack 3 the bit pattern 1,1 is present which then is transformed into bit pattern 1,0 at the output of rack 3, which bit pattern is transmitted to the input of rack 4 and then transformed into 0,0. Thus, a next rack connected to the output of rack 4 would receive the same bit pattern as rack 1 so that an ambiguity would exist with respect to the addressing of rack 1 and such a fifth rack. In consequence thereof, the use of two address lines defining a two-bit pattern limits the system to the use of four racks. Since all devices include as device selection means the NAND-­ gate 31 which produces an enable signal when it receives a logic 1 at each of its inputs, and since the inputs of the NAND-gate 31 are connected to the address lines A, B at the input connection 23, the NAND-gate 31 of the third rack would receive the bit pattern 1,1 and thus enable rack 3 if at the input of rack 1 the bit pattern 0,0 is present, as shown in Fig. 3. Below the racks 1 to 4 shown in Fig. 3 the bit patterns are indicated which are present at the inputs A, B of the respective racks. These bit patterns show, for example, that for addressing the last rack 4 the bit pattern 1,0 at the input of the first rack must be present. If a rack is correctly addressed and the module selection unit 33 enabled so that it produces a module enabling signal in response to the address connected thereto from address lines C, D, E, the enabling signal of module selection unit 33 is connected to two OR-gates 34 and 35, the first one being in­ serted into a line 36, 36′ connecting the transmitting line T and an input port of module 15, whereas the second OR-gate 35 is inserted into a line 37, 37′ connecting an output port of module 15 to the receiving line A. When both gates 34 and 35 are open and the module 15 is present, module 15 is able to respond to signals transmitted from centre monitoring station 10. The line sections 36′ and 37′ are connected by a gate arrange­ ment comprised of gates 41, 42, 43 which form a switch connecting the said line sections 36′ and 37′. If a module 15 is connected as shown in the left portion of Fig. 2, input lines to gates 41 and 42 are grounded so that these gates 41, 42 form a bar, whereas gate 43 is held open in order to pass the signal emitted by module 15. If, however, an address module is missing as in the right portion of Fig. 2, the inputs of gates 41, 42 are no more grounded but connected to a high level by pull-up-resistors 44 and 45, respectively. Thereby, gates 41, 42 and 43 are opened so that a direct connection between the transmitting and receiving lines exist, returning the transmitted signal immediately to the centre monitoring station 10. This centre monitoring station senses this immediate return of the transmitted signal and thus senses the missing of the addressed module. Into the portion of the transmitting line T connecting input connection 23 to output connection 24, an OR-gate 51 is inserted which is closed by the enable signal produced by the device selecting NAND-gate 31 and connected to one input of OR-Gate 51 via inverter 52. Thus, the transfer of the transmitted signal to the output connection 24 is blocked when the rack is addressed, whereas it can pass on to the output connection 24 and thus to the next rack if the present rack is not addressed. This means that in any case the transmitted signal is blocked within the addressed device and not passed to the output connection thereof. The transmitting line T is further connected to NAND-gate 53 which has its other input connected to a line 54 which is grounded when another rack is connected, and which is also connected via pull-up-resistor 55 to a high voltage level. Gate 53 forms again a switch which is non conducting when another rack is connected to the output connection 24, but which is closed and thus connects the transmitting line T via gates 56, 57 and 58 to the receiving line, so that a trans­ mitted signal is again immediately sent back to the centre monitoring station in order to indicate that the addressed rack is missing. The arrangement of gates 56, 57, 58 has the purpose to block that transmitted signal if the addressed rack is the last one in the series. Summing up, the illustrated embodiment of the invention allows a series connection of four racks, each containing up to eight modules. All racks have the same construction, the address of the racks being determined exclusively by their respective position in the series. Similarly, the addresses of the modules are determined only by their position in the rack. Switch means between the transmitting and receiving lines allow to recognize whether or not an addressed rack and/or module is present. If a rack or a module fails in its operation, this may be recognized by a missing or defective response signal. Since no addressing errors can be made and the existence and function of address modules is monitored, the embodiment forms a very secure system which is especially appropriate for medical purposes. As mentioned before, the inventive system for addressing serially connected devices and their racks used in the embodi­ ment according to Fig. 2, may be extended to address a greater number of devices. If the scheme shown in Fig. 3 is extended to four address lines, 2×4=8 different addresses may be produced as shown in Fig. 4. Generally, if N address lines are used, 2N different addresses may be produced if all lines are cyclically displaced and in one of said lines an inverter is inserted.

Claims: 1. Digitally adressable electronic device including input means (23) having at least first and second contacts (R, T) provided for the connnection of a receiving line and a transmitting line, respectively, a first plurality of contacts (A, B) provided for the connection of a plurality of address lines to which an address signal may be applied in parallel, and second plurality of contacts (C, D, E) for the connection of a further plurality of address lines to which a further address signal may be applied in parallel, device selection means (31) having a plurality of inputs each one thereof being connected to one of the contacts forming said first plurality of contacts (A, B) for receiving said address signal and an output (32) for providing in response to said address signal a control signal enabling or disabling signal transmission via said receiving and transmitting lines, characterized in that said device has the same design as at least one further device to which it may be connected; that it includes output means (24) having at least first and second contacts (R′, T′) electrically connected to said first and second contacts (R, T) of said input means (23), respectively, and a third plurality of contacts (A′, B′) connected to said first plurality, of contacts (A, B) in such a way that at least two contacts of said third plurality are interchanged with respect to the corresponding contacts of said first plurality so that the address signal at the output means (24) is different from the address signal fed to the input means (23); that the device selection means (31) responds to a unique bit pattern which is common for all similar devices; that an inverter (25) is inserted in at least one of the lines connecting said first plurality of contacts (A, B) with third plurality of contacts (A′, B′); that it includes a plurality of modules (15) and module selection means (33) for selectively activating each one of said modules, said module selection means (33) including a plurality of inputs connected to said second plurality of contacts (C, D, E) and a plurality of outputs each one being connected to one of said modules (15), said module selection means (33) providing an enable signal to a selected one of said modules (15) in response to a predetermined further address signal; that each module (15) is connected to said first and second contacts (R, T) of said input means (23) via a module gate (34, 35) which is opened by said enable signal; and that first switch means (41, 42, 43) are connected between each module (15) and the associated module gate (34, 35), said first switch means (41, 42, 43) establishing a connection (34, 41, 42, 43, 35, 58) between the first and second contacts (R, T) in response to said enable signal and to the detection of the missing of the addressed module. 2. Device according to claim 1, characterized in that second switch means (53, 56, 57, 58) are connected between the second contact (T′) of said output means (24) and the first contact (R) of said input means (23), said second switch means (53, 56, 57, 58) establishing a connection between said contacts (T′, R) in response to the detection of the missing of a futher device connected to said output means (24). 3. Device according to claim 2, characterized in that third switch means (51) are connected to the respective second contacts (T, T′) of said input means (23) and output means (24), said third switch means (51) establishing a connection between said second contacts (T, T′) in response to the control signal being a disenabling signal. 4. Device according to any one of the preceding claims, characterized in that the first and second pluralities of contacts are each comprised of a series of N contacts, each contact bearing a designation n, wherein N is an integer and n is defined by 1>n>N, each n th contact of the first plurality being directly connected to the (n+1) th contact of the second plurality with the exception of the N th contact of the first plurality which is connected to the 1 st contact of the second plurality via an inverter. 5. Device according to any one of the preceding claims, characterized in that the device selection means (31) generates the enable signal if all bits of the address signal applied to its input have the same value. 6. Device according to any one of the preceding claims, characterized in that at least one of said switch means is a gate means. 7. Device according to any one of the preceding claims, characterized in that it constitues a medical monitoring device (1) which can be connected in series to other similar devices (12, 13, 14) and whose input can be connected to a central monitoring station (10). 8. Device according to claim 7, characterized in that it has the form of a cabinet or rack into which seperate modules (15) can be inserted for the supervision of special body functions, as for example heart activity, breathing rate, brain activity etc.

Inventors: KAISER, WINFRIED, SALFELD, PETER, SCHOBER, ANDREAS
Applicants: HEWLETT-PACKARD GMBH
Application year: 1988
Main classification: G06F12
IPC codes: H04Q9, G06F12, G06F13