Abstract: In a local area network all communication nodes are connected only to a centrally located star network coupler, but data is transmitted from one communication node to the next active communication node in a sequence defined by a ring protocol. The star network coupler may be implemented by switches capable of connecting a receiver for one communication node to a transmitter for the next communication node or to a bypass line for the next communication node. However, preferably the star network coupler comprises a selective multiplexer for each of the nodes. Each selective multiplexer has inputs connected to all of the communication nodes to receive therefrom transmission data and a line status signal indicating communication activity with each node so that inactive nodes can be bypassed.

Abstract: A cyclic redundancy check generator for a high speed data bus is capable of outputting frames of data and cyclic redundancy check bits concatenated together without any additional space or time delay between frames while operating at a normal clock speed. Data to be transmitted is parallel loaded into series-connected registers via multiplexers connected between the registers. The multiplexers also provide parallel loading of the cyclic redundancy check bits for a frame of data from a look-ahead cyclic redundancy check logic circuit. The output of the logic circuit is also connected to a cyclic redundancy check register. The logic circuit has inputs connected to the final series-connected data register and the cyclic redundancy check register.

Abstract: The invention comprises a system for scrambling, transmitting and descrambling the video portion of a TV signal. In the preferred embodiment two serial memories (charge coupled devices) are utilized to store data representing selected portions of the video to be scrambled. The charge coupled devices are selectively clocked to interchange portions of video, with the point at which the interchange occurs determined by a code pattern generator and changing in a predetermined manner. The point of interchange is updated or changed as determined by a code pattern generator and changing every three lines of the TV signal. Descrambling is accomplished by an identical hardware arrangement with the exception that the code pattern generator at the descrambler is synchronized with the code pattern generator in the scrambler. Synchronizing information can be transmitted to the descrambler in any convenient fashion including inserting the data in an unused video line of the vertical retrace interval.

Abstract: A protective relay for protecting a power system from sub-synchronous current oscillations. The protective relay determines both the amplitude and frequency of sub-synchronous current oscillations occurring in the power system. A series of logic relationships, based in part on the parameters of the power system, are implemented by the protective relay such that when the frequency and amplitude of the sub-synchronous oscillation signal satisfy these relationships a trip signal is produced.