Browse Prior Art Database

Character Loading & Refreshing for Video Displays

IP.com Disclosure Number: IPCOM000076665D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Cockrell, HH: AUTHOR

Abstract

Described is a simplified technique for transferring bytes from a shift register serving as a primary-buffer memory, to the address input of a character-generating read-only memory (CGROM). The CGROM may be viewed as a translator which converts an N bit code, representing an informational byte or character, to an M bit code which is used to intensify light points within an M by P dot matrix used for the video display of any symbol, including alphanumeric characters, which can be depicted by a particular combination of dots within an M by P dot matrix. The N bit address is generally a subset of the required number of CGROM address bits, where the remaining address bits equal log(2) P and these remaining address bits are derived from, e.g., some periodic source such as the video raster generator.

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Character Loading & Refreshing for Video Displays

Described is a simplified technique for transferring bytes from a shift register serving as a primary-buffer memory, to the address input of a character- generating read-only memory (CGROM). The CGROM may be viewed as a translator which converts an N bit code, representing an informational byte or character, to an M bit code which is used to intensify light points within an M by P dot matrix used for the video display of any symbol, including alphanumeric characters, which can be depicted by a particular combination of dots within an M by P dot matrix. The N bit address is generally a subset of the required number of CGROM address bits, where the remaining address bits equal log(2) P and these remaining address bits are derived from, e.g., some periodic source such as the video raster generator.

In the generalized case, L, the length (number of serial cells) of the shift register serving as the primary-buffer memory is chosen to be an integer multiple of the number of symbols in one row of the displayed symbol field, and thus if the displayed symbol field contains R rows and C columns, then L=(R+i)C where i=0, 1, 2, 3,.... The serial shift register of length L is paralleled N times to provide a maximum storage capacity of L bytes -- each byte composed of N bits. The M by P dot matrix is a subset of an H by V space matrix where H>M and V>P by the amounts which provide acceptable spacing between columns and between rows of the displayed symbol field. If the M by P matrix is oriented horizontally by vertically, respectively, and a horizontal raster scan is employed in the video display assembly, then the L length shift register must be advanced at least C times per horizontal line of the raster scan. In this arrangement, the shift register is advanced exactly C times per horizontal line of the raster scan; therefore, except for the trivial case where R=1 and i=0 (i.e., L=C), the shift register is generally not positioned to address the CGROM(s). Hence, an auxiliary -- or spin-off shift register of serial cell length, at least C, and paralleled appropriately, is employed. The V dimension of the space matrix is then chosen to meet an acceptable spacing between rows of the displayed symbol field plus to meet the criterion V=1+L/C, where V is the number of raster-scan lines assigned the vertical dimension of the space matrix. In most video display units employing a horizontal scan-line raster, this criterion is not restrictive since a vertical height and a vertical linerarity adjustment are available to gracefully alter the vertical spacing of the raster lines. In this disclosure, the exact number of horizontal scan lines in the raster is Z, where Z=jL/C, and j=l, 2, 3, .... Therefore, it is apparent that -- from an initial state, the L length shift register can transfer a block of C bytes of data into the spin-off shift register, whose length is >/- C, at a periodic rate, and further the...