Character and video mode control circuit

Details Character and video mode control circuit Character and video mode control circuit

1983-04-04

1986-09-23

Curtis, Marshall M.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340735, 340745, 340703, G09G 100

Patent

active

046138560

ABSTRACT:
An electrical circuit is described that requires a reduced number of data bits for character-address and video-mode information by using a predetermined bit combination of the video-mode information as part of the character-address information. Character-address and video-mode information is output from a random access memory (RAM) to a character read only memory (ROM) and a video-mode detection circuit that produces outputs to enable video-mode circuits in the video control circuitry. One output of the video-mode detection circuit is coupled to an address input of the character ROM that has characters divided into two character sets. A predetermined bit combination of the video-mode information produces an output from the video-mode detection circuit that selects one of the character sets while the other bit combinations produce an output from the detection circuit that selects the other character set. In this way, character-address and video-mode information having n data bits can produce character and video-mode outputs that normally require n+1 data bits.

REFERENCES:
patent: 3603966 (1971-09-01), Gregg
patent: 3909792 (1975-09-01), Harris
patent: 4297693 (1981-10-01), Parsons
patent: 4398190 (1983-08-01), Long
patent: 4408198 (1983-10-01), Kudirka
patent: 4429306 (1984-01-01), Macanley

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