US 4,374,395 AGranted

Video system with picture information and logic signal multiplexing

AssigneeTexas Instruments Incorporated

InventorsCarlo L. Herrmann, Granville E. Ott

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Abstract

A color video signal generator includes means for selectively generating either color difference information or logic levels from the same output pins. The color video signal generator is employed in a video system which outputs either the internally generated video signal or an externally generated video signal depending on whether the color difference information or the logic levels are generated. This invention has application to video terminals and small computing systems which employ video displays to enable selective display of internally generated pictures or externally generated pictures or selective overlap of such pictures. This invention also has application to integrated circuit pin minimization by enabling an analog and a digital signal to be multiplexed on the same pin.

Claims14

Dependent claims

A luminance signal generator having a first output terminal, for generating at said first output terminal a line synchronization signal having a predetermined fixed first voltage during a first predetermined period of a repetitive video line interval and for generating at said first output terminal a brightness signal having a voltage in the range between a second voltage and a third voltage during a second predetermined period of said repetitive video line interval, said range between said second voltage and said third voltage extending to the limits of said brightness signal voltages and not including said first voltage;

and
two color difference signal generators, each having a second output terminal and each responsive to an external video override signal, each for generating at said second output terminal a color difference signal having a voltage in said range between said second voltage and said third voltage during said second predetermined period, said range between said second voltage and said third voltage extending to the limits of said color difference signal voltages, and each for generating at said second output terminal an external video enable signal having said first voltage when said external video override signal is received.

A video generator system comprising:

a video generator, responsive to an external video override signal, for generating a plurality of signals indicative of picture information, each having a voltage in a range between a first voltage and a second voltage, said range between said first voltage and said second voltage extending to the limits of said picture information signals, at least one of said signals being indicative of synchronization information having a predetermined fixed third voltage outside said range between said first voltage and said second voltage during a predetermined repetitive portion thereof and at least one of said signals being indicative of an external video mode having said third voltage when said external video override signal is received;
a video encoding means for encoding said plurality of signals indicative of picture information into a single internal composite video signal;
and
a video switching means responsive to said external video mode indicative signal, said internal composite video signal and an external composite video signal encoded in the same format as said internal composite video signal, for outputting said internal composite video signal when said external video mode indicative signal has a voltage in said range between said first voltage and said second voltage and for outputting said external composite video signal when said external video mode indicative signal has said third voltage.

1 more element

Dependencies are inferred from the claim text.