Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1985-02-11
1986-12-23
Ng, Jin F.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358 22, H04N 504
Patent
active
046315888
ABSTRACT:
An apparatus, and its method, for overlaying a computer display on a video signal, having a video signal receiving circuit, a sync strip circuit connected to said video signal receiving circuit for stripping the sync pulses from the video signal, and a display control circuit for generating display control pulses. A phase locked loop circuit is provided for locking the display control pulses in phase with sync pulses stripped from the video signal when the video signal is present, and for controlling the display control means to generate display control pulses at a selected rate when the video signal is absent. A vertical drive pulse generating circuit generates vertical drive pulses in phase with selected ones of the sync pulses stripped from the video signal when the video signal is present, and generates vertical drive pulses after a set number of generated display control pulses when the video signal is absent. A computer display generator circuit generates computer display signals under the control of the display control pulses and the vertical drive pulses. A combining circuit combines the video signal with the generated computer display signals when the video signal is present, and blocks the subsequent combining of later received video signals with the generated computer display signals for a set time when the video signal is absent, allowing the phase locked loop circuit to lock the display control pulses in phase with the sync pulses of the reestablished, later received video signals.
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Barnes Lawrence C.
Mankedick Robert G.
Dugas Edward
Gonzalez Floyd A.
Hawk Jr. Wilbert
NCR Corporation
Ng Jin F.
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