Patent GB-1311503-A (GB)
Title: Display device including roll and crawl capabilities
IPC: G09G5/34
Filed: 1970-04-24
Abstract: 1311503 Cathode-ray tube displays A B DICK CO 24 April 1970 [9 June 1969] 19902/70 Heading H4T In a data display arrangement lines of characters are made to " roll " upwardly from the bottom towards the top of the display and the characters themselves are made to " crawl " in lines from right to left across the display the speed of both the " roll " and " crawl " being adjustable. The characters are produced by bright-up of the beam of a display cathode-ray tube (operating at normal television frequencies) in the form of a 9 x 11 dot matrix (Fig. 5) a " guard-band " of five dot spaces being provided for inter-character spacing and of three dot spaces for interline spacing. Referring to Fig. 2, a core memory 40 is loaded with character data from a keyboard 14 (or a tape reader 12) at addresses determined by the position of a cursor (displayed at half the character intensity) so that, in the read mode in normal operation, the stored data is displayed in respective corresponding positions on the tube screen. In the normal read mode the memory 40 is addressed under the control of character and line counters 24, 26 which are stepped-on by the outputs, at full count, of X and Y matrix counters 34, 36 the data read-out being supplied via a register 42 and decoder 44 to a video selector 30. The X and Y matrix counters 34, 36 (Fig. 4, not shown) determine a 12 x 14 matrix (i.e. the 9 x 12 character matrix plus the guard bands) and control a character generator 38 which generates the bright-up (video) signals required to produce each of the characters the system is capable of displaying-e.g. 64 Alpha-Numeric characters. The signals corresponding to the output of decoder 44 are then passed by video selector 30 to a mixer 50 in which they are combined with the cursor signal and the output of the mixer then forms the bright-up (video) signals for a conventional TV monitor 57 the scanning of which is controlled by an external synch. source 16. The display comprises 16 lines each of 24 characters. Thus, in the normal read mode, the characters are read out of the memory 40 and displayed in positions corresponding to respective positions in the memory under the control of the character and line counters 24, 26 which are advanced, when the X and Y matrix generators 34, 36 reach full count, by one count for each character and for each line respectively which are displayed, both counters being reset by the vertical synch. signals of the system. In the " roll " or " crawl" read mode the counters 24 and 26 are not reset at the beginning of each field and of " roll " or " crawl " keys on the keyboard (Figs. 9A to 9D, none shown) operate to introduce a substitute row-column counter the output of which supplies a count of the number of lines (in the " roll " mode) and of the number of characters (in the " crawl " mode) and provides the resetting pulses for the X and Y matrix generators. The operation then consists of periodically incrementing the count in counter 26 or counter 24 (for " roll " or " crawl " respectively) by one count so that the core memory 40 is addressed at a different address and the line of characters or the individual character are displayed at positions which are one line position up the screen or one character position to the left of the position at which they would otherwise be displayed. The effect of the resulting motion is enhanced by blanking the top and bottom character row positions and the extreme left and right hand side character column positions and in order to avoid the appearance of jumping, the start of the first line to be displayed may be progressively delayed by intervals of 14 down to 1 horizontal synch. pulses in a repeating cycle the period of which may be varied to vary the speed of the display motion. This speed may be selected by keys to be fast or slow but if no speed is selected an intermediate speed results. New data may be entered into the memory during the 16th line or 24th character display periods, i.e. when the display is blanked, to produce a continuous " roll " or " crawl " effect. The displayed data may be made to flicker by means of a flush control circuit 46 in response to non-viewable, stored control data. Specification 1,251,689 is referred to.