Crt character display apparatus employing double height algorithm

Abstract

A data display arrangement in which each of a number of different characters displayed on a CRT is defined by selected dots of a dot matrix. The stored character information from which character generating signals are produced is in the form of corresponding memory cell bit matrix. Such character information is read-out once in a number of successive scanning lines of each field to display the character normal height, and hitherto has been read-out twice in a number of successive pairs of scanning lines of each field to display the character double height. The invention provides a 'double height algorithm' which modifies the read-out for double height character display such that part of a memory cell is read-out once and part is read-out twice. This results in a non-linear expansion of a double height character the effect of which is to maintain the visual baseline of a character row. With respect to a simple expansion, the enlarged character is 'pushed down' by a number of scanning lines thus maintaining the baseline. Any part of a character below the baseline is 'compressed' into the space below it. FIG. 2 shows examples of displayed characters.