MAGNETIC DATA STORAGE AND LOGIC DEVICE FOR DIGITAL DATA PROCESSING SYSTEM

Abstract: A magnetic storage device (10) having an integral magnetic address decoding mechanism includes a ladder-shaped element of magnetic material having a plurality of rungs, including a first input rung (A), last output rungs (J and K), and a plurality of rungs (B through H) therebetween, all of the rungs being supported between two sidebars (11 and 12). Each pair of rungs, with the adjacent sidebars, defines a window (21 through 27). An input wire is wound around the input rung, and address input wires (P through S) are wound around alternating rungs between the input rung and one rung before the output rung. Address pulses are applied to the address input wires to establish magnetic flux around the windows so as to propagate magnetic flux generated by the input pulse to the output rung. The direction of flux from the input pulse and the address pulses determine the value of the data written. When the data is read, pulses are applied to the address input wires and to the input wire which generates flux in a predetermined direction. Depending on the direction of the previously-written magnetic flux at the output rung, the flux due to the input pulse may either reinforce the flux through the output rung or cause it to change direction. If the flux direction is changed an output voltage pulse is generated in the output wire, otherwise no pulse is generated, which identifies the value of the data, which had previously been written.

Description: MAGNETIC DATA STORAGE AND LOGIC DEVICE FOR DIGITAL DATA PROCESSING SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of devices for storing digital data in a digital data processing system, and more specifically to high-speed random access storage devices in which data is stored in a stationary magnetic medium. 2. Description of the Prior Art Data is stored in' digital data processing systems, that is, computer systems, in the form of binary digits, or bits. Typical modern-day computer systems store data both electrically and magnetically. Electrical storage is accomplished by means of MOS memory circuits, in which each data bit is represented by an electrical charge in a capacitor, or flip-flops, in which the conducting/non¬ conducting state of two anti-parallel connected inverters determines the data value. Electrical storage is volatile, that is, it requires the constant presence of electric power; otherwise, if the power is turned off, the data is erased. Magnetic storage is typically now used for mass back-up of large amounts of data that are transferred as needed to and from the electrical storage devices in the computer. In current magnetic storage devices, the data is stored as magnetic flux changes on a moving magnetic medium, either a rotating disk or a linearly-moving tape. Since the data is stored magnetically, data is not erased if the power is turned off. However, accessing (that is, reading or writing) a particular item of data stored magnetically typically takes significantly longer than for data stored electically. In current magnetic storage devices, to access a particular item of data on the disk or tape, the read/write head must be moved to the portion of the medium containing the data. This mechanical operation takes a relatively long time, and so the average access time for magnetic storage is typically much longer than the average access time for electical storage devices. To reduce the overhead time represented by the delay, a large amount of data is stored in a particular region of the medium and transferred at one time from that region. Accordingly, current magnetic storage devices are not used for random-access storage and retrieval of individual items of data. In the past, however, generally before the development of MOS memory circuits, magnetic storage was used for random access storage. At the time, flip-flop circuits were relatively expensive and so they were used, if at all, only for small amounts of data. The magnetic storage devices that were used in digital data processing systems were coincident current magnetic devices for random access data storage. In such devices, data was not stored in moving magnetic media; instead, coincident current magnetic storage devices stored data bits in toroidal cores of magnetic material, which were organized in two-dimensional matrices having a plurality of rows and columns. A separate wire was strung through each row and column and a particular core could be accessed by energizing the row and column-wires which intersected at that core. The current which energized each of the row and column wires was insufficient to affect the magnetic state of a core, and so the magnetic state of the other cores in the ' row and column through which the wires ran was not affected by the current. However, the current in both wires together was sufficient to affect the magnetic state of a core, and so the magnetic state of the core at the intersection of the two energized lines was set accordingly. The selection of the wires to be energized was made by conventional electrical switching circuitry. Prior to the advent of large-scale integration of electronic components onto monolithic integrated circuits, ferrite logic circuit elements were devised which could . perform some logic operations. One such element, a "laddie" (for "ladder logic") comprised a ladder-shaped element of magnetic material. A circuit including laddies is ilXu-strated in U.S. Patent No. 4,192,013, issued March 4, 1980 to Keats, et al., for Safety Circuits For Coupling Laddies In Cascade, and a description of the use of laddies in logic circuits is presented in C. J. Dakin, et al. , Circuits For Digital Equipment, Chapter 8, at pages 174-179 (Ilife Books, Ldt., London, 1967). As an example of the use of a laddie, to perform an AND function (in an AND function, the output signal from the device has an asserted condition only if all of the input signals to the device also have asserted conditions) on four input signals, a laddie is used having ten rungs supported between two sidebars, the rungs forming nine "windows. Wires for various input and control signals were wound on the laddie as follows. Wires for the four input signals, which carried the four signals to be ANDed, were wound on the second, fourth, sixth and eighth rungs, an "evaluate" input wire was wound on the first rung, an output wire was wound on the tenth rung, and a reset input wire was wound around a sidebar through the first, third, fifth, seventh and ninth windows. In operation, a pulse was applied to the reset input, which generated magnetic flux which established magnetic circuits around the first, third, fifth, seventh and ninth windows. In this initial condition, small magnetic circuits were also established in the portions of the sidebars adjacent the second, fourth, sixth and eighth windows. Input signals in the form of pulses were applied to the respective input wires, simultaneously with the assertion of a signal on the evaluate input wire. The assertion of an input caused the generation of magnetic flux which caused the reinforcement and/or establishment of a magnetic circuit around the ' adjacent windows; that is, * for example, the pulse applied to the first input wire reinforced the already- existing magnetic circuit around the first window, and caused the establishment of a magnetic circuit around the second window, eliminating the small magnetic circuits in the sidebars adjacent the window. If pulses were applied to all of the input wires, all of the small magnetic circuits were eliminated in the sidebars and magnetic circuits were established around all of the windows. The portions of the magnetic circuits along the sidebars were such that they would essentially cancel each other out along the length of the sidebar. In this condition, the pulse on the evaluate wire also generated magnetic flux which established a magnetic circuit through the sidebars and the outermost rungs, that is, the first and tenth rungs, of the laddie. Depending on the respective directions of the flux due to the set input pulse andd thre; flux due to the last hold input pulse, the set input pulse would cause a net increase or decrease in the flux in the tenth rung of the laddie, which would be sensed in the output winding around the tenth rung as an electrical voltage pulse. If, on the other hand, if pulses were not applied to one or more of the input wires, the small magnetic circuits in the adjacent sidebars would remain, and the magnetic flux from the set input pulse would be forced to go through the next rung closer to the first rung. In this situation, little or no flux from the set input pulse would be applied to-the tenth rung, and so no change in flux would be sensed i the output winding. SUMMARY OF THE INVENTION The invention provides a new and improved magnetic data storage device having an integral addressing element that uses magnetic elements to perform the address decoding. In brief, a ladder-shaped element of magnetic material is used having a plurality of rungs, including a first, input, rung, a last, output rung, and a plurality of rungs therebetween, all of the rungs being supported between two sidebars. Each pair of rungs, with the adjacent sidebars, defines a window. An input wire is wound around the input rung, and address input wires are wound around alternating rungs between the input rung and one rung before the output rung. A reset wire is wound around one sidebar through the windows that are to adjacent each rung supporting an address input wire and upstream thereof, that is, through the windows toward the input r.ung. A pulse applied to the reset wire initializes magnetic circuits around the windows adjacent to and upstream of the address input wires. When address pulses are applied to the address input wires, if the magnetic circuits established thereby are properly established, the storage element is addressed, that is, the magnetic flux established by the input pulse at the input rung will be propagated to the output rung. The direction of flux from the input pulse and the address pulses determine the value of the data written. When the data is read, the device is again initialized by means of a pulse at the reset wire. Pulses are then applied to the address input wires and a pulse is placed on the input wire which generates flux in a predetermined direction. Depending on the direction of the current comprising the address input pulses and the direction of the flux at the output rung, the flux due to the input pulse may either reinforce the flux through the output rung or cause it to change direction. If the flux direction is changed an output voltage pulse is generated in the output wire, which may be sensed by conventional sensing circuits and thereby identify the direction of the flux, and thus the value of the data, which had previously been written. The data is then written back into the device. BRIEF DESCRIPTION OF THE DRAWINGS This invention is pointed out with particularity in the appended claims. The above and further advantages of this invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of a data storage device constructed in accordance the invention; and Fig. 2 is a schematic view of a second embodiment of the data storage device depicted in Fig. 1. DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT With reference to Fig. 1, a data storage device 10 constructed in accordance with the invention includes two sidebars 11 and 12 having a plurality of rungs extending therebetween. Ten rungs, labeled A through K, are shown in the embodiment depicted in Fig. 1. A set input wire 13, which receives a SET INPUT signal, is wound on rung A, which constitutes an input rung and an output wire 14 is wound on output rungs J and K. The seven rungs between rung A and rung K, that is, rungs B through J, will allow for decoding four address input signals on address wires P through S. Address wire P is wound around rung B, address wire Q is wound around rung D, address wire R is wound around rung F, and address wire S is wound around rung H. It will be apparent that additional address signals may be decoded by increasing the number of rungs. The sidebars and rungs define nine windows 20 through 28. A reset wire 30, which carries a RESET initializing signal, is wound around the sidebar 12 through windows 20, 22, 24, and 26. That is, the reset wire is wound around the sidebar and through the windows that are upstream, that is towards the input rung, of the rungs B, D, F, and H around T O which the address wires P, Q, R, and S, are wound. Between the windows 20, 22, 24, and 26, the reset wire 30 is disposed substantially parallel to sidebar 12. The sidebars and rungs are constructed of a magnetic material of any known type. Rung K should of a remanent material to hold flux that is generated during a writing operation. Rung J may also be of a remanent material, but it is preferable that rungs A through I, and the sidebars, not be constructed of a remanent material. If rungs A through I and sidebars 11 and 12 are constructed of non- remanent material, it will be apparent that a reset wire may not be necessary. In operation, if data is to be written into the s ' torage device, the RESET signal, in the form of a pulse, is first applied to reset wire 30. If the current flows in the direction indicated by the arrowheads on line 30, magnetic flux is generated in the sidebar 12 so as to generate magnetic circuits in a clockwise direction around windows 20, 22, 24 and 26, with the flux present in the sidebars 11 and 12 and rungs A through H. Taking the specific example of the magnetic circuit around window 20, the current in the reset wire 30 causes magnetic flux to be generated in the portion of the sidebar 12 between rungs A and B, with the direction of the flux being longitundinal through sidebar 12 and to the left as shown in Fig. 1. Since along the portions of sidebar 12 adjacent windows 21, 23 and 25 the reset wire 30 is relatively parallel to sidebar 12, no magnetic flux is generated longitudinally in the portions of sidebar 12 adjacent those windows. Thus, to complete the respective magnetic circuits, taking the flux generated in the portion of sidebar 12 adjacent window 20 as an example, the flux continues upwardly through rung A, to the right through the portion of sidebar 11 between rungs A and B, and down through rung B, to finally join with the flux to the left in the portion of sidebar 12 between rungs B and A, resulting in a complete magnetic circuit defined by flux having a clockwise direction around window 20. The magnetic circuits around windows 22, 24, and 26 are similar. After the RESET pulse is applied, address signals and a SET INPUT signal are applied, in the form of pulses, to the address wires P, Q, R, and S and set input wire 13. If current is applied to the address wires in the direction indicated by the arrowheads, magnetic circuits are established around windows 21, 23, 25 and 27. with the magnetic flux being in a counter-clockwise direction. In this situation, the flux from the SET INPUT data pulse applied to rung A is reflected in rungs J and K, with the direction of the current comprising the SET INPUT pulse determining the direction of the flux. Af-tec the pulses representing the SET INPUT and address signals-, are removed, the magnetic flux remains. To read the data bit stored in the storage device 10, the RESET pulse is again applied to initialize the rungs A through H and the portions of sidebars 11 and 12 therebetween. The RESET pulse has no affect on the magnetic flux in rungs J and K, and therefore that flux represents the data stored in the data storage device" 10. After the RESET pulse, the pulses representing the address signals P through S and the SET INPUT signal are applied. The current for the pulses representing the address signals is applied as depicted in Fig. 1 to generate magnetic circuits around windows 20 through 27 as described above in connection with writing of the data into the storage device. The current for the SET INPUT and address pulses, however, have a predetermined direction. Depending on the direction of the magnetic flux in rungs J and K, the SET INPUT pulse will cause the magnetization to either remain in the same direction or flip to the opposite direction. If there is no change in the direction of magnetic flux in rungs J and K, no output signal will be generated in the output winding. However, if the SET INPUT pulse causes the magnetic flux in rungs J and K to change an output signal will be generated in the output wire. The value of the data stored in the storage device, which is determined by the direction of magnetic flux in rungs J and K, thus can be determined by whether or not a signal is generated in the output wire and the direction of current in the SET INPUT and address pulses. As is apparent to those skilled in the art, the direction, of current flow through the address wires P through S determines whether data is stored in or rea'd from the storage device 10. More specifically, the magnetization of the various portions of the sidebars 11 and 12 and of rungs A through H determines whether magnetic flux from the SET INPUT signal on wire 13 reaches rungs J and K. There are several ways of varying the addresses of a plurality of storage devices 10 used in a single data storage unit so that they are individually addressable. For example, the address input wires P through S can be connected to a source of address signals so that if one storage device is accessed, that is, read or written, the current for at least 1 one of the address wires for the other stora . ge devices is in another direction than is depicted in Fig. 1. In this condition, a magnetic circuit will be established around one of the windows 21, 23, 25 or 27 with the flux in a different direction than is required for accessing of the storage device 10_ This may also be accomplished by having the address wires P through S for the diverse storage devices in a storage unit be wound around the respective rungs in different directions. For example, if a storage device had address wire Q wound around rung D such that it was situated in front of rung D, rather'than behind it, and behind i sidebar 11, then (assuming the direction of current in the other wires was the same as depicted in Fig. 1) that storage device would not be accessed unless the current through that wire was in the opposite direction than that depicted by the arrow in Fig. 1. Accordingly, the storage devices can be distinguished by the direction of the current in the winding of the address wires P through S around rungs B, D, F and H. The storage device depicted in Fig. 1 can be fabricated individually, or a large number of them can be fabricated at simultaneously in an array using thin film techniques described in our copending U.S. Patent Application Ser. No. 06/763,844, filed August 8, 1985, entitled Data Storage Apparatus For Digital Data Processing System, which is incorporated herein by reference. As is apparent, the storage device depicted in Fig. 1 stores but one data bit, and a plurality of them must be accessed in unison, on separate input and output wires, to form a data word. A-partial illustration of a second embodiment of the invention, which stores a plurality of data bits which can be accessed together as a word, is depicted in Fig. 2. With reference to Fig. 2, a storage device 100 is illustrated whose left-hand portion, the addressing and enabling portion, is the same- as for the storage device 10 in Fig. 1. (In the embodiment depicted in Fig. 2, the reset wire 30 is not shown.) Storage device 100 includes sidebars 111 and 112 and rungs A through K, a wire 13 for a SET INPUT signal, and wires P through S for address input signals. Sidebars 111 and 112 and rungs A through K are similar to sidebars 11 and 12 in storage device 10 (Fig. 1), forming windows 120 though 128. Window 128 is larger than corresponding window 28 in Fig. 1 so as to accommodate four storage elements 130 through 133, each of which stores one data bit of a four bit data word. As depicted in Fig. 2, each of the storage elements 130 through 133 includes two congruent U—shaped members nA and nB (where "n" is an integer from 130 through 133) of magnetic material which depend from upper sidebar 111. The U-shaped members for each storage element 130 through 133 depend from sidebar 111 in window 128. The width of sidebar 111 adjacent window 128 is somewhat narrower than in the other regions of the storage device. Members nA are preferably formed of a remanent material. Each storage element 130 through 133 also includes a bit select wire nC and a sense wire nD (where "n" is an integer from 130 through 133) around corresponding U-shaped members nB and nA/ respectively. In operation, a pulse is first applied to the reset wire (not shown) in the same manner as described above in connection with storage device 10 (Fig. 1) to initialize magnetic circuits around windows 120, 122, 124 and 126. The address input pulses are applied to address input wires P through S and a SET INPUT pulse is applied to set input wire 13 as described below. If the current for the address pulses is in the proper direction, as described above in connection with Fig. 1, the magnetic flux generated as a result of the SET INPUT pulse will extend around the right-hand portion of window 128. The write operation for the embodiment depicted in Fig. 2 is performed in two sequential portions. In the first portion, the data bits are written which are represented by flux in one direction. This is followed by the second portion in which the data bits are written which are represented by flux in the other direction. The current representing the SET INPUT and address pulses change direction to provide flux in the two directions required to represent the data. In both operations, concurrently with the address pulses and the first SET INPUT pulse, bit select pulses are applied to selected ones of the bit select wires 130C through 133C. The current forming the bit select pulses is in a direction to generate flux in members 130B through 133B and the adjacent portions of sidebar 111 which would oppose the flux generated in sidebar 111 by the SET INPUT pulse. This forces the flux from the SET INPUT pulse, which would otherwise go through the portions of sidebar 111 adjacent members 130B through 133B, to go through members 130A through 133A associated with the bit select wires 130C through 133C which are energized by BIT SELECT pulses. When the SET INPUT pulse is turned off, since members 130A through 133A are formed of a remanent material, the flux remains. Thus, data represented by flux in the direction established by the SET INPUT pulse during the first part of the write operation is stored in the storage elements 130 through 133 whose bit select pulses have been energized. In the second portion of the write operation, the current forming the SET INPUT pulse is in the opposite direction, so as to generate magnetic flux in sidebar 111 in the opposite direction. Bit select pulses are applied to the bit select wires 130C through 133C which did not receive such pulses during the first portion. The current forming the bit select pules is in the direction to generate a magnetic flux in the portions of the sidebar 111 so as to oppose the the flux generated in sidebar 111 by the SET INPUT pulse. This forces the flux from the SET INPUT pulse, which would otherwise go through the portions of sidebar 111 adjacent members 130B through 133B, to instead go through memers 130A through 133A whose associated bit select wires 130C through 133C are energized by BIT SELECT pulses. When the SET INPUT pulse is turned off, since members 130A through 133A are formed of a remanent material, the flux remains. Thus, data represented by flux in the direction established by the SET INPUT pulse during the second part of the write operation is stored in the storage elements 130 through 133 whose bit select pulses have been energized. i 9 In a reading operation, only one portion is required to detect a flip of the magnetic flux stored in each of the members 130A through 133A. To perform a reading operation, the SET INPUT pulse is applied to wire 13 and BIT SELECT pulses are applied to bit select wires 130C through 133C. The address input signals must be maintained in the proper directions to allow flux generated by the SET INPUT pulse to pass to the portion of sidebar 111 adjacent storage members 130 through 133, which is necessary if their contents are to be read. The flux generated by the BIT SELECT pulses in sidebar 111 must oppose the flux generated there by the SET INPUT pulse so as to direct the flux generated by the. SET INPUT pulse through respective members 130A through 133A. Depending on the direction of the pre-existing flux which was previously written into each member, the flux from the SET INPUT pulse may cause a flip in the direction of the flux in the member, which would cause a signal to be generated in the associated sense wire 130D through 133D. If the previously-written flux was in the opposite direction from the applied flux due to the SET INPUT pulse, such a signal will be generated, otherwise no signal will be generated. The direction of the flux stored in the members 130A through 133A, which represents the value of the data, is identified by whether or not a signal is generated in the sense wires 130D through 133D. Thereafter, a write operation is performed to rewrite the data into the device. The reduced cross-sectional area of the sidebar 111 in thfi: region adjacent window 128 provides for a greater flux density of the magnetic flux in that region. This assists in: the establishment and sensing the presence of magnetic circuits in storage elements 130 and 133 during writing and reading operations, respectively. The foregoing description has been limited to a specific embodiment of this invention. It will be apparent, however, that variations and modifications may be made to the invention, with the' attainment of some or all of the advantages of the invention. Therefore, it is the object of the appended claims to cover all such variations and modifications as come within the true spirit and scope of the invention. What is claimed as new and desired to be secured by Letters Patent of the United States is:

Claims: CLAIMS 1. An addressable storage device comprising: A. a magnetic element formed of in the shape of a ladder having a pair of sidebars and a plurality of rungs, one end comprising an input end and the other end comprising a -storage end, each pair of rungs defining a window; B. a reset wire wound around one of said sidebars and extending through every alternate window except for the window adjacent said storage end; C a plurality of address wire-s around alternating rungs f om said input end, to said output end; D. input wire means wound around said rung at said input end; and E. output wire means wound around said rung at said storage end.

Inventors: COPE DAVID, SPLETTER GARY, COPE, DAVID, SPLETTER, GARY
Applicants: MRAM INC, MRAM INC.
Application year: 1987
Main classification: G11C8
IPC codes: G11C8, G11C11