Abstract: A dual mode encoding/decoding technique for use in digital systems wherein transmitted digital words are limited, on average, to an alotted number of bits. The transmitted digital words are coded into first and second modes. The first coding mode utilizes predictive differential coding to provide a precision which can be greater than that obtainable by coding information solely with the allotted number of bits, while the second mode assures at least a minimum precision for the allotted number of bits. The first coding mode is transmitted as long as a preselected precision is provided. If not, the second coding mode is transmitted. In the disclosed embodiment, the dual mode encoding/decoding technique is applied to the transmission of color video signals.

Abstract: An interactive graphics transmission system for use, illustratively, in video teleconferencing is described which advantageously reduces the amount of transmission bandwidth and user effort required to transmit changing graphical information. This is accomplished by first transmitting a full image of the graphic followed only by the changes which a conferee makes to that graphic. Those changes are determined by sensing the tilt of a light pen and the location of its tip, which is closest to the graphic, as a conferee manipulates the pen to change the graphic. The tilt of the pen primarily determines the mode in which the light pen is used. The mode information, in conjunction with the location of the pen's tip, is used to generate an instruction which specifies the way in which the graphic is to be changed, e.g., whether information is to be added to, deleted from or emphasized in a graphic. In addition, the location of the pen's tip specifies the address of that portion of the graphic that is to be changed.

Abstract: Communication between a plurality of data stations (100(1)-100(N)) serially interconnected by way of a line (101) arranged in a ring is provided by bit interleaved data packets. A control station generates framing signals to designate the start of each packet, staggering the packets so that only one packet header appears on the line at a time. Processing equipment (114) at each station monitors all the headers, seizing "empty" packets if the station has a data burst to send and reading the data burst if the packet is addressed thereto.

Abstract: Communication between a plurality of data terminals (101(1) to 101(b)) serially interconnected with a main terminal (102) is provided by data frames or packets having a data portion for accommodating a burst of data preceeded by a header portion for accommodating address data followed by an empty/full "flag" bit indicating whether the addressee station has withdrawn the data burst. If a terminal has a data burst to send, it locates an empty packet, inserts the addressee designation in the packet subsequent to any prior address that the packet might contain, interposes delay in the passage therethrough of the packet so that the duration is increased to accommodate the new address and overwrites the data burst into the data portion. The main terminal detects when the data burst is withdrawn and signals the originating terminal to remove the data delay.