Patent GB-1289955-A (GB)
IPC: G09G1/10
Filed: 1970-01-20
Abstract: 1289955 Cathode-ray tube displays J V CARREFOUR J C MERLIN and P PITARD 20 Jan 1970 [22 Jan 1969] 2623/70 Heading H4T In a system for displaying characters on the screen of a cathode-ray tube each character being formed by a group of vectors with each vector represented by a binary vector word of which one bit controls beam blanking and unblanking and the other bits define selected ones of a finite number of predetermined directions, groups of vector words defining respective characters are stored in a character store at addresses set up in an associated address register the address of each character having a larger number of bits than the number of bits in the vector word defining each vector and in order to change the character corresponding to a given address a number of (fictitious) addresses equal to the number of vector words required in the formation of the new character.are produced by operating the same number of keys on a keyboard the corresponding symbols &c. of which are represented in "Flexowriter" (Registered Trade Mark) code by binary words the last four bits of each of which form a respective vector word of the new character, such vector words being temporarily stored and then transferred to the character store at the address of the character to be changed this latter address being produced by selecting a particular keyboard symbol the whole of the code of which forms the address in binary notation.  The invention is described in connection with a cathode-ray tube display in which the characters are formed by deflecting the beam in a sequence of selected ones of the directions shown in Fig. 1 (depending on the particular character) each deflection step, a maximum of sixteen of which are allowed for any character, having unit magnitude along the X or Y axes and #2 times this magnitude along the diagonals and being defined by the three digit binary word indicated. Figs. 2a, and 2b show the formation of the characters A and α respectively together with the binary words defining each deflection step in terms of the deflection direction, the three most significant bits and in terms of the beam blanking requirement, the least significant bit, of which "1" indicated unblanking and "0" blanking. The whole display is produced by the arrangement shown in Fig. 4, in which coded signals are supplied via a buffer register 3 to an address register 4 (unless a character is to be changed when a detector 18 in response to a particular function combination signal interrupts the path to register (4) and thence via a character store 5, buffer register 7, regenerating store 6 (to produce persistence during display) series-to-parallel converter 9 and a register 10 to control the beam blanking and the deflections necessary to produce the required character. When a character is to be changed a particular function combination signal from the keyboard operates via detector 18 to interrupt the path to register 4 and instead routs the output of buffer 3 to a selection circuit 23. Sixteen of the fictitious addresses (referred to above) are now transmitted and selection circuit 23 removes the first two bits of these 6 bit addresses and retains only the least significant four bits. These are sent to a shift register 25 and thence to buffer register 7 (for transfer to character store 5) and to counter 26 which counts sixteen groups of four bits and then resets detector 18 so that incoming signals again pass to register 4. A second function combination signal (which may be one or more "carriage return" signals) is now transmitted and this sets character location register 19 to the address of the character to be changed (the address in store 6 and on the screen). The new character which is now stored in character store 5 is now produced at the location previously occupied by the former character.