Patent GB-1309698-A (GB)
Title: Symbol display system
IPC: G09G5/30
Filed: 1970-03-19
Abstract: 1309698 Cathode-ray tube displays PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 March 1970 [22 March 1969] 13318/70 Heading H4T In an arrangement in which characters, symbols &c. are produced or the screen of a cathode-ray display tube by modulation (brightup or blanking) of a line scanned raster the modulation control signals, which are produced by a character generator, are supplied to the beam intensity control means through a circuit which, under the control of signals derived from counters which count the number of vertical lines per character, the number of characters per line, the number of (horizontal scan) lines in a line of characters and the number of lines of lines of characters per field, may be operated selectively to invert the modulation signals. Thus selected characters or selected areas of the whole display may be accentuated by being produced as black traces in a field of white traces or vice-versa. Other facilities include the production of horizontal and vertical lines of contrasting brightness between rows and columns of characters respectively and the control of the brightness of the overall picture background. Fig. 1, shows the display of a cursor C indicating a blank space and Fig. 2 a cursor C indicating the character B for the case of black characters on a white background and Fig. 3 shows the cursor C in the case of white characters on a black background. Fig. 4 shows how information originating from the user (e.g. produced by a keyboard) may be distinguished from received information by displaying the former (first two lines) as black traces on a white background and the latter as white traces on a black background. Figs. 5 and 6 show the display of vertical and horizontal lines and Fig. 7, shows how the interspace between lines  of character may be accentuated in the case of black traces on a white background, by pro-  ducing the interspace 2 in an intermediate shade of grey. Fig. 8, shows the general arrangement in which data supplied to a memory SP from a data processor over lines E/A or from a keyboard Ta through a line T is fed to a character generator ZG which is controlled by a control stage St supplied with clock pulses from clock TG and with the outputs of counters which count the number of columns per characters (counter Spz) the character being formed in a matrix of eight vertical (column) and seven horizontal dots, the number of characters per line (counter ZchZ), the number of line scans per character (counter LZ) and the number of lines of characters per field (counter ZlZ). The outputs of these counters are also fed to a blanking signal (A) generator A the output of which is supplied to a gate P together with the output signal B of the character generator ZG fed via the controlled inverting stage CI. The character and blanking signals BA are then combined in a mixer M with synchronizing signals S produced in a generator Sy and the composite signal BAS is utilized to produce the required display on a monitor television type display T.V. Fig. 9 shows the arrangement for producing the cursor C of Figs. 1 to 6 under the control of the keyboard by means of contacts C1, C2 which set-up the desired horizontal and vertical position of the cursor in terms of a count in counters ZC1, ZC2. The outputs of the counters are then compared in stages VC1, VC2 with the outputs of counters ZchZ and ZCZ and when equality is detected an output signal is supplied via AND gate U to the cursor control stage CSt which also receives the output of counter LZ (to establish the vertical dimension of the cursor). Control stage CSt then operates the controlled inverting stage CI so that at the position in which the cursor is to be displayed the signal B is inverted to B. The arrangement of Fig. 9 is described in greater detail with reference, to Fig. 10 (not shown), and the manner in which the other facilities which the invention affords are realized by the production of suitable signals for controlling the inverting stage CI are described with reference to Figs. 11 to 13 (not shown).