Patent GB-1169856-A (GB)
Title: Pattern Generator
IPC: G09G1/14
Filed: 1968-03-08
Abstract: 1,169,856. Cathode - ray tube displays. ALPHANUMERIC Inc. 8 March, 1968 [3 April, 1967], No. 11397/68. Heading H4T. In an Alpha-Numeric character display system each character is deemed to be divided into a plurality of areas each of which is divisible into adjacent linear regions the addresses of each end of which are specified (in a rectangular co-ordinate system) by coded indicia (specifically digital words) the characters being reproduced by utilizing the coded indicia to unblank the beam of a cathode-ray display tube as it is deflected vertically between the end-point addresses for each of the (horizontally) adjacent linear regions and the operations being such that linear regions having the same horizontal position but lying in different ones of the areas into which the characters are deemed to be divided (e.g. having different vertical positions) are not reproduced during the same vertical deflection. Thus, referring to Fig. 1, the character, comprising an upper case " G " deemed to be divided into areas A 1 , A 2 , A 3  which are reproduced in this order by vertical scanning between coloumns C8 to C60 the beam being unblanked only during the scanning of the black linear regions in area A 1  (defined by the columns and row members C and R respectively) after which the beam, whilst blanked, is positioned at column C63 to reproduce area A 2  whilst being stepped unblanked back towards columns C42. Area A 3  is then reproduced by positioning the beam at column.C48 and stepping it back, unblanked, to columns C18. The digital words specifying the characters may define the absolute addresses of the start and end elements of each linear region or may define such, after the initial start address, in terms of the increment (+ or -) by which this address must be modified to give the next address. The words, including operational control words are derived from a memory M (Fig. 3A) and in addition to providing operational control outputs via a function decoder FD, provide control outputs, CNK specifying the column number (C number), SVR specifying the start value (R number) of a linear region and EVR specifying the end value (R number) of a linear region. The CNK output is utilized as shown in Fig. 2B to control the horizontal position of the beam of the display tube CRT and the SVR output positions the (blanked) beam at the starting R number. Assuming the vertical scan flip-flop VS to be in the set condition its output VD unblanks the beam of the tube and triggers the vertical sawtooth generator STG so that a vertical scan commences. The set output of VS also conditions an AND gate G2 to pass pulses from an oscillator OSC to a column element counter CEK which is preset via AND circuit GS2 with the start value signal SVR. The count in CEK is fed to a column element comparator CEC supplied with the end value signal EVR and on equality between reached an output signal ICN resets the flip-flop VS which on the disappearance of the VD output causes the beam to be blanked and fly-back to commence and by means of its reset output VD<SP>1</SP> conditions an AND circuit G3 to pass oscillator pulses to a retrace counter RTK. The latter " overflow " after a period deemed suitable for the circuit to " settle down " and its output SVS then sets flip-flop VS to commence a new vertical trace. The ICN signal is also supplied to the column number counter CNK, (Fig. 2A) so that it is stepped on one count unless a further function control input specifies some other column, as e.g. changing from one to another of the areas A 1 , A 2 , A 3 . The apparatus continues to operate in this manner until the whole of the character has been reproduced in the sequence of areas A 1 , A 2 , A 3 , as described earlier. In the operational mode in which the initial start address is modified by the algebraic addition of an appropriate increment to produce all subsequent end addresses the incremental data being equivalent to an end element address is substituted directly therefor and stored in end value register EVR and there is no need to pre-set the columns element counter CEK with start element addresses, since column element comparator CEC compares a number representing the number of elements in an increment (now indicated by the EVR signal) with a running count from zero in counter CEK. After each equality indicated by the column element comparator CEC counter CEK must be cleared to zero and this is done by feeding the ICN signal via a delay network to the clear input of the counter. The characters reproduced on the screen of the tube are photographed on film FLM and the latter is then utilized in the preparation of a printing block.