Digital Equipment Corporation

Lsi Logic Corporation

Willem A Engelse

Todd R Comins

Michael D Rostoker

D Tony Stelliga

Dave Paolino

John A Visser

Gary V Vacon

Stephen D Metzger

Jeffrey A Lomicka

A random number generating apparatus for an interface unit of a Carrier Sense with Multiple Access and Collision Detect (CSMA/CD) Ethernet data network. The interface unit includes a transmit backoff unit for implementing a backoff algorithm in response to a network collision signal and a random number. The apparatus comprises a dual mode random number generator and a multiplexer for switching the random number generator between modes in accordance with the serial address bits of a data packet being processed by the interface unit. The random number generator includes a 25 stage linear feedback shift register. The multiplexer has two signal inputs connected to outputs of the 18th and 22nd stages of the shift register respectively, a switch input connected to receive the serial address bits and an output connected in circuit to an input of the shift register.

Random number generating apparatus for an interface unit of a carrier

A circuit for receiving and decoding Manchester-encoded communication signals such as those used in an Ethernet network. The circuit uses a single local reference clock signal to clock a shift register that temporarily stores samples of the incoming signal. A window pointer selects a particular bit of the shift register as the current output bit; the value of the window pointer is maintained by a feedback loop which tracks any phase error in the incoming signal, that the output data remains in phase with the incoming signal. The combined functions of a Manchester-decoder and retiming circuit are thus provided in a simple circuit.

Synchronous decoder for self-clocking signals

Automatic tracking of the topology of an extended local area network by augmenting a station address list kept by a bridge with a list of repeater numbers and repeater port numbers. The bridge periodically iterates through its list of stations to select a station address. The selected address table is forwarded to all of the repeaters connected to the bridge. The repeaters watch for the selected address appearing as a source address in a message on one of their ports. If the address is seen, they report the repeater port number back to the bridge. Because the repeaters are interconnected such that a predetermined port number is always used as the common port between repeaters, any possible ambiguities are eliminated.

Automatic association of local area network station addresses with a

A computer graphics technique for rendering shaded areas by using pseudo-random noise localized to image boundaries is disclosed. Calculated pixel values are initially generated using an arithmetic accuracy larger than the word size of an associated bitmap memory. The calculated pixel values thus have a most significant portion, corresponding to the portion which is to be stored in bitmap memory, and a least significant portion, corresponding to the additional accuracy. Pseudo-random noise, preferably generated by a linear feedback shift register, is then added to some or all of the least significant portion, and the carry output from this operation is added to the most significant portion. The most significant portion is then written into bitmap memory. Changes in the value of the integer portion thus occur with increased frequency as the distance to an intensity boundary decreases, since the random noise causes the dithering to occur with increased frequency. The result is a more natural display than would otherwise be available with a given bitmap memory word size.

Rendering shaded areas with boundary-localized pseudo-random noise

A terminal server architecture includes a central processing unit (CPU), a data movement module, local area network (LAN) interface and a plurality of connected terminals. The CPU manages pointers to data using command status registers to instruct the data movement module to actually perform data movement between the terminals and the LAN.

Terminal server architecture

Method and apparatus for rendering a smooth-shaded graphics primitive vertical series of horizontal pixel spans which extend between beginning and trailing edges of the primitive, the pixel locations being spaced from each other by selected distances dX and dY. The apparatus produces X and Y addresses of the first and last pixels in the beginning span of the primitive and the number of spans in the primitive. Also produced are step values (dX/dY) indicating the slopes of the beginning and trailing edges, and a beginning intensity value for the first pixel in the beginning span. DX is added to the X address of each pixel in each span to determine the X address of the next pixel in that span and one of the step values is added to the X address of the first pixel in each span to calculate the X address of the first pixel in the next span of the primitive. In addition, the other of the step values is added to the X address of the last pixel in each span of the primitive to calculate the X address of the last pixel in the next span of the primitive. The distance dY is added to the Y address of each span to calculate the Y address of the next span until the number of spans has been rendered. One or more intensity values is cumulatively added to the beginning intensity value to calculate the intensity value for the next pixel.

Method and apparatus for displaying smooth-shaded objects

A graphics subsystem (10) employs an image memory (12) that includes an on-screen part (44) and an off-screen part (46). The locations of the on-screen memory (44) are continually scanned to provide data to be displayed on a display device (16). The off-screen part (46) stores data that represent image segments that have been occluded by windowing. To transfer data between the on-screen part (44) and the off-screen part (46), an address generator (24) generates a sequence of two-dimensional addresses representing the two-dimensional positions of the pixels whose data are to be transferred. These addresses are converted to one-dimensional addresses by a simple circuit consisting of multiplexers (26 and 28), adders (30 and 32) and a multiplier (34).

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Townsend, MA, United States of America

Willem A Engelse