Image display apparatus

Claim 1

In an image display apparatus comprising sync signal generation means for generating sync signal pulses, display timing signal generation means, image memory means for storing image element data constituting a pattern, having a predetermined raster line number of raster scan lines, of a letter or a character or a drawing, a video circuit for converting said image element data into a video signal according to signals from said sync and display timing signal generation means and display means for displaying the pattern of a letter or a character or a drawing according to the output of said video circuit, an improved programmable memory address generation unit for generating raster addresses that designates selected raster lines in a selected pattern stored in the image memory means to be repeated a predetermined repeat number of times, said unit comprising: logic means, coupled to receive the sync signal pulses and a raster line designating signal, for transmitting selected sync pulses only when said raster line designating signal is set; a counter, coupled to receive said transmitted selected sync pulses, for generating a count signal having a value incremented upon receipt of each selected sync signal pulse and reset when said value is equal to a selected number, said count signal specifying a raster line in the selected pattern; a plurality of programmable registers for storing a set of integers designating raster scan lines in the selected pattern to be repeated for the predetermined repeat number of selected sync signal pulses; and raster redesignating means, coupled to receive said count signal and said sync signal pulses, and coupled to said registers, for resetting said raster line designating signal for said predetermined repeat number of sync signal pulses to prevent the incrementing of said count signal for said predetermined repeat number of sync signal pulses when the value of the count signal is equal to the value of one the integers in said set so that the raster scan line designated by the count signal is redesignated said predetermined repeat number of times.