Abstract: A memory mapping unit which permits a computer to run programs designed to provide 32-bit or 24-bit address signals to address a 32-bit addressable memory. When a CPU generates a 32-bit address, that address is passed through to provide a 32-bit physical address. However, when the CPU generates a 24-bit address, the most significant bits are processed by the memory mapping unit to provide a remapped 32-bit physical address. The memory mapping unit is implemented on a single semiconductor chip using gate-array technology.

Abstract: A disk drive which includes an automatic parking brake for retaining the driver arm in a predetermined position when power is removed from the disk drive. The brake is mounted externally to the driver arm, reducing the weight of the driver arm. The brake consists of a spring loaded member held in place during operation of the disk drive by a solenoid acting as an electromagnet. When power is cut off, the solenoid releases the member and the spring biases it against the driver arm and forces the driver arm to a parked position.

Abstract: An enclosure having an improved seam for inhibiting passage of electromagnetic radiation through the enclosure is described. The enclosure having a housing and a removable cover are joined at its respective edges. A plurality of spaced-apart tabs extend from an edge and slideably engage a plurality of slots which are formed on an interior surface adjacent to a corresponding mating edge. A domed projection on each tab slides into recessed cavities located on each slot to form a tight mechanical connection. The enclosure has a metal-coated interior surface and mating surface, wherein the tabs and slots operate to electrically couple the cover to the housing.

Abstract: A floppy disk drive controller interface implemented as an integrated circuit on a single semi-conductor chip. The controller connects to a host computer data bus and one or more floppy disk drives. Based upon clocking and control signals received from a digital computer, the controller generates serial encoded data for recording on a floppy disk and receives serial encoded data previously recorded on a floppy disk. The controller comprises a read control circuit including a read data register, write control means including a write data register, a mode register, a status register, state latches, a decoder and special function registers. The controller operates by the setting and clearing of the state latches and reading or writing the mode register, the status register, the special function registers, the read data register and the write data register. The setting of a state latch and accessing of a register is done simultaneously.

Abstract: A circuit for accepting serial data from a source meant for video display and displaying it on a liquid crystal display. The data is converted to parallel and is stored in address locations corresponding to four quadrants of a display screen. An input counter controls the writing of data to the memory, while an independent output counter controls the reading of data from the memory and its display on the liquid crystal screen display.

Abstract: A disk drive which includes an actuator motor whose magnets and iron path are mounted on the arm assembly to act as a counter weight. The coil of the actuator motor is mounted to the base of the disk drive with the iron path disposed around the coil and the iron core disposed through the center of the coil and all are mounted on the iron path and face the coils. By utilizing the iron path and magnets as a counterbalance, the total mass of the arm is reduced, reducing the inertia of the arm and of the power requirements of the actuator motor to move the arm.

Abstract: A local area network is disclosed including apparatus and methods for transferring data between a plurality of data processing resources ("agents") coupled to a cable. In the preferred embodiment, a plurality of agents are coupled to a common cable for data transmission and reception. An agent newly coupled to the cable dynamically assigns itself a unique address on the cable to which other agents may send data. Once an agent has been assigned a final address, it may then transmit to, and receive data from, other agents on the cable. An agent desiring to send data to a receiving agent follows a three step handshake, wherein the sending agent transmits an "RTS" signal and within a predetermined time must receive a "CTS" signal from the receiving agent. The sending agent then transmits a data frame within a predetermined time after the CTS signal is received. The failure to detect a return CTS signal within the predetermined time denotes a collision condition.

Abstract: A local area network is disclosed including apparatus and methods for transferring data between a plurality of data processing resources ("agents") coupled to a cable. In the preferred embodiment, a plurality of agents are coupled to a common cable for data transmission and reception. An agent newly coupled to the cable dynamically assigns itself a unique address on the cable to which other agents may send data. Once an agent has been assigned a final address, it may then transmit to, and receive data from, other agents on the cable. An agent desiring to send data to a receiving agent follows a three step handshake, wherein the sending agent transmits an "RTS" signal and within a predetermined time must receive a "CTS"signal from the receiving agent. The sending agent then transmits a data frame within a predetermined time after the CTS signal is received. The failure to detect a return CTS signal within the predetermined time denotes a collision condition.

Abstract: Apparatus and methods are disclosed which are most advantageously used in conjunction with a digital computer to provide improved graphics capability. These techniques permit the representation and manipulation of any arbitrarily shaped image in terms of "inversion points". Inversion points defining a region are sorted and stored such that the region shape may be regenerated at a later time from the inversion points. Means are provided to compare existing regions and new regions to be displayed, and region operators are provided to specify a precedence between the existing and new regions. Thus, new regions are appropriately "clipped" such that only portions of a new region may actually be displayed to achieve the desired graphic representation.

Abstract: A cursor control device having particular application to a computer display system is disclosed. The cursor control includes a unitary frame, having a domed portion substantially surrounding and retaining a ball which is free to rotate. X-Y position indicating means are provided, such that rotation of the ball provides signals indicative of X-Y positions on the display system. The ball is free to "float" in the vertical direction within the dome, and thereby maintain good surface contact. X-Y positions are established by movement of the control device over a surface. A display system and method is disclosed for use in conjunction with the cursor control device, which permits a user to select command options simply by movement of the displayed cursor over a "pull-down" menu bar.

Abstract: A cursor control device having particular application to a computer display system is disclosed. The cursor control includes a unitary frame, having a domed portion substantially surrounding and retaining a ball which is free to rotate. X-Y position indicating means are provided, such that rotation of the ball provides signals indicative of X-Y positions on the display system. The ball is free to "float" in the vertical direction within the dome, and thereby maintain good surface contact. X-Y positions are established by movement of the control device over a surface. A display system and method is disclosed for use in conjunction with the cursor control device, which permits a user to select command options simply by movement of the displayed cursor over a "pull-down" menu bar.