Browse Prior Art Database

True Half Indexing on a Raster Display

IP.com Disclosure Number: IPCOM000046757D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Bohrer, KA: AUTHOR [+2]

Abstract

This technique provides an accurate and true display of half-indexed characters on a raster scan cathode ray tube (CRT). The half-indexed characters are depicted on the CRT display in the same positional relationship relative to surrounding characters as they would appear on a document as a result of printing. Fig. 1 gives an overview of a typical alphanumeric display architecture with a half-indexing controller added. The character font memory is accessed once for each character slice. The font memory data bits are then modified for attributes by setting and resetting bits, serialized, and sent to the display as the video signal. The half-indexing controller contains storage and logic and is inserted prior to the serializer. It affects the overall system minimally by delaying video one character slice time.

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True Half Indexing on a Raster Display

This technique provides an accurate and true display of half-indexed characters on a raster scan cathode ray tube (CRT). The half-indexed characters are depicted on the CRT display in the same positional relationship relative to surrounding characters as they would appear on a document as a result of printing. Fig. 1 gives an overview of a typical alphanumeric display architecture with a half-indexing controller added. The character font memory is accessed once for each character slice. The font memory data bits are then modified for attributes by setting and resetting bits, serialized, and sent to the display as the video signal. The half-indexing controller contains storage and logic and is inserted prior to the serializer. It affects the overall system minimally by delaying video one character slice time. Assuming an eight-pel wide, 16-pel high character box and a vertical scan alphanumeric display adapter, the half-indexing controller processes the character box image data (16-bit word) as two separate eight-bit bytes one after the other. The byte representative of the top half of one vertical slice of the character is followed by a byte representative of the bottom half of one vertical slice of the character. This simplifies the half-indexing controller and allows the parallel-to-serial conversion to take place on half character boundaries. Fig. 2 shows the logic of the half-indexing controller. The controller includes three eight-bit (half character box) registers (lower, middle, and upper), control logic to determine which register is to be loaded with the half character font information, and multiplexer/latch logic to separate the font 16-bit word into eight-bit top and bottom half character bytes. Table 1 includes a cycle-by-cycle illustration of the register contents for each of the following three display operations: (1) nonhalf-indexing characters "A" and "B" continuously, (2) nonhalf-indexed character "A" followed by a half-index up "B" followed by a nonhalf-indexed character "C", and (3) nonhalf-index...