GB1293506A - Improvements in or relating to video display systems - Google Patents

Abstract

1293506 Cathode-ray tube displays SUMLOCK ANITA ELECTRONICS Ltd 19 April 1971 [23 March 1970] 25035/71 Heading H4T In a system for displaying digital data signals in the form of characters on a raster scanned colour television monitor, digital data are transferred from a buffer memory to a character shift register which addresses a character memory the output of which is converted to a serial video bit stream by a video generator which is also controlled by a colour decoder coupled to the character shift register so that the characters are displayed in colour. The display 1 comprises four fields 2, each of eight characters divided into four lines 3 of twenty characters each. The input data is in the form of 7-bit ASCII code words which are stored in a buffer memory 6 providing five fields each of eighty words (characters). One of the data fields is selected and the first line (20 characters) is inserted in a recirculating character shift register 8. A read-only memory 13 has a five-by-seven matrix providing a 35-dot representation for each different character which can be displayed and this memory is addressed by each word in the character shift register in turn and by a character control generator 15 to provide a 5-line parallel output corresponding to the top line of the selected character matrices. After the character shift register has been recirculated the process is repeated but reading out the second line of each character matrix, and the process is repeated further until all seven matrix lines have been read out. The parallel outputs are converted to serial form in video generator 12 which supplies red, green and blue outputs to a colour CRT display 1 under control of a colour decoder 14. A monochrome output 230 is also provided. A timing signal generator 9 provides clock pulses for the character shift register 8 and main memory 6 and signals for controlling the transfer of data and for providing the raster scan of the display are also derived from this generator. Two modes of operation are possible, in the first mode sixteen codes not required for character representation are utilized to indicate the colour of the characters and backgrounds. The use of any of these codes replaces one of the character words causing a gap in the display and controls the colour of all succeeding characters or backgrounds as appropriate. In the second mode the background is black and the colour of the character is determined by its characteristic, i.e. capital letters, lower ease letters (displayed as capitals but in a different colour.), numerals and punctuation, and communication characters are displayed in different colours.