Patent GB-1235295-A (GB)
Title: Character-generating circuit for a character-writing cathode-ray tube
IPC: G09G1/10
Filed: 1968-09-03
Abstract: 1,235,295. Cathode-ray tube displays. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 3 Sept., 1968 [2 Sept., 1967], No. 41797/68. Heading H4T. In an arrangement for producing Alpha- Numeric characters on the screen of a cathoderay tube by deflecting the beam between selected points on a point matrix individual deflection control elements are provided for the X and Y co-ordinates of each point in the matrix the elements appertaining to the points in a character to be traced being rendered effective in succession in a constant order by means which " scans " all the elements in the same order but selectively " skips " elements not appertaining to points in the character. The characters are produced in a matrix comprising vertical rows of 5, 3, 5, 3, 5 points (Fig. 1a) the deflection control elements appertaining to which are " scanned " in a sequence commencing at the point P/A20 and in an order such that for any one character successive points designated either A or B have increasing numerical values. Some of the points have two or more references, e.g. B3, B11; A6, B18; B10, A12, A18 and identify points which, in the production of a character are impinged more than once by the electron beam. Thus in tracing the numeral " 3 " (Fig. 1b the beam, which is first directed to point P/A20 (the starting matrix point for all characters) by auxiliary character positioning means (not shown) is then directed in sequence from point A1, A16 to the other points shown in full black in ascending numerical order, the " empty " " circles indicating points not used for this character and the points A1, A16 and B10, B12 being impinged twice during the tracing operation. During this tracing the beam is blanked during the steps between points A2 and A4 and between A11 and B10, A12. The sequence of steps for tracing the letter " E " are shown in Fig.1c. Each character is specified by a six-unit binary code which sets six bi-stable triggers (not shown) and the outputs of which E1, E1<SP>1</SP>; E2, E2<SP>1</SP> &c. (Fig. 2a) are applied to the base electrodes of transistor pairs T11, T11<SP>1</SP>; T21, T21<SP>1</SP> &c. The first five of the latter pairs are connected via further transistor pairs T12, T12<SP>1</SP>; T22, T22<SP>1</SP> to matrix rows S1, S1<SP>1</SP>; S2, S2<SP>1</SP> &c. which are connected via diodes D1, D2 &c. to a plurality (only one shown) of column lines B(0, 32) connected to the base electrodes of individual pairs of transistors (only one pair shown) T(0), T(32). The latter pairs of transis. tors are controlled by the output of the transistor pair T61, T61<SP>1</SP> and the arrangement operates such that, depending on the digital inputs to the latter pair, a significant output is obtained on either line Z(0) or line Z(32). Thus the number of column lines required is equal to half the number of characters to be selected. The various output lines Z(0), Z(32) are connected to the appropriate rows of a character generator ZAM, Fig. 2b, having column lines A1, B1, C1; A2, B2, C2 &c. connected at cross-points to the rows by means of diodes (indicated by oblique dashes). The various characters are indicated at the left of the row with which they are associated and the outputs on the triplets A1, B1, C1 &c. represent the deflection magnitudes and the beam bright-up requirement for such step (up to a maximum of twenty steps) in the tracing of the characters the steps being in ascending numerical order. ' The deflection magnitudes A, B are fed to respective NAND gates U1 U2 ... U20 (only five shown), Fig. 3, which are so connected via further NAND gates N1, N2 ... N20 and the stages K1,K2...K20 (only five shown) of a shift counter (controlled by two preliminary stages VK1, VK1 supplied with a start signal ST and clock stepping pulses from a timing generator TG) that the shift signals which each stage of the counter normally supplies to the succeeding stage are caused to " skip " over those stages the associated A1,B1 &c. input to which is not significant i.e. does not represent a matrix point to be impinged by the beam. The outputs of the various counter stages are then supplied to pairs of NAND gates U11, U12; U21, U22 &c. having, as second inputs, the deflection magnitudes A1, B1, A2, B2, &c. and the outputs of which are supplied via pairs of resistors W111, W112,W211,W221, weighted respectively in accordance with the X and Y deflection magnitudes, to the X and Y deflection summing amplifiers SVx and SVy respectively. For the blanking of unrequired trace portions the C outputs of the character generator ZAM are combined as shown in Fig. 4 via AND gates UH, NOR gates NH and a NAND gate NEH the output of which is supplied to the beam intensity control electrode. The character generator ZAM (which is incompletely shown) provides outputs for the tracing of both upper and lower case characters and provides, via a column line t, an input to a trigger Kt (Fig. 3) which supplies a deflection quantity to the Y summing amplifier SVy via a resistor Wt to shift the vertical position of the character so that characters with sub-scripts comprising other characters may be traced. Also, by injecting a deflection quantity proportional to the Y deflection into the X deflection the characters may be produced in italics. Figs. 5a and 5b show the X and Y deflection steps respectively and Fig. 5e the beam blanking requirements for tracing the numeral " 3 " of Fig. 1b These result in the production of the numeral as a series of bright points (the black dots of Fig. 1b but by connecting low-pass filters between the outputs of the summing amplifiers and the X and Y deflection circuits the step waveforms may be connected to the form shown in broken lines so that the lines connecting the bright points are produced as visible traces.