GB1436517A - Character generator - Google Patents

Abstract

1436517 Printers INTERNATIONAL BUSINESS MACHINES CORP 18 Sept 1974 [23 Oct 1973] 40600/74 Heading G4H A front memory holding the matrix decompositions of characters is addressed with a combination of a base address derived from a character code and the output of a register decrementable to indicate a column within the character matrix. In a zerographic printer the image of a page of characters is produced on a rotating copy drum by a rotating hexagonal mirror which deflects a laser beam to scan parallel to the drum axis to build up the page as a raster as the drum rotates. Assuming that the lines of characters are produced circumferentially of the drum, the beam thus produces one column of the decomposition of one character as a matrix of dots in one line before going on to the next line. As each line of characters is thus dealt with in a given scan line of the beam, a counter 65 accesses from a control register 60 a word respective to this line of characters. This word specifies the character position being dealt with and a column count (for the character matrix). These items are placed in registers 67, 68 respectively and the former is used to address a page memory 57 holding the page of characters to be printed to obtain the required character code. This code, together with status bits to select type style, addresses a ROM table 70 to obtain a base address and the number of columns in the character matrix, these items being placed in registers 82, 84 respectively. At the beginning of the character, register 84 is gated to a register 87 (under control of a zero-detector 85 responsive to register 68) otherwise register 68 is gated to register 87 with decrementing at 104. Register 87 is subtracted from register 82 at 90 to address a font memory 92 to obtain the matrix column which is serialized at 97 and used to modulate the laser beam at 38. The contents of registers 87, 67 are stored into the addressed word of control register 60, the contents of register 67 being incremented by one at 100 at the end of a character (under control of a onedetector 101 responsive to register 68) to subsequently select the next character position in the line. If the lines of characters are to be produced parallel to the drum axis (so that the lase scan line goes along the line of characters) the words in control register 60 relate to columns of characters (perpendicular to the lines) rather than lines,the status bits 76 are adjusted to access, via table 70, rotated fonts in font memory 92, and the incrementing at 100 is by the number of characters per line rather than by one. Space codes are provided as necessary in the page memory 57 but to save long sequences of them, "end of row", "end of scan" and "end of page" codes are also used. Two fewer bits may be used in table 70 to specify the number of columns in the character matrix by use of a 2-bit counter. Font memory 92 may use compression coding.