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Display Adapter Design for Fast Proportionally Spaced Characters

IP.com Disclosure Number: IPCOM000120863D
Original Publication Date: 1991-Jun-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 8 page(s) / 310K

Publishing Venue

IBM

Related People

Cheselka, H: AUTHOR [+4]

Abstract

A new structure for a display adapter that combines the best features of all-points-addressable (APA) and character generator designs has been developed. It can do proportionally spaced characters with the performance of hardware character generators doing simpler fixed cell size characters. The basic approach is to put stable, well-defined function in hardware.

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This is the abbreviated version, containing approximately 26% of the total text.

Display Adapter Design for Fast Proportionally Spaced Characters

      A new structure for a display adapter that combines the
best features of all-points-addressable (APA) and character generator
designs has been developed.  It can do proportionally spaced
characters with the performance of hardware character generators
doing simpler fixed cell size characters.  The basic approach is to
put stable, well-defined function in hardware.

      Proportionally spaced characters are hard to implement in
character generator type display adapters.  They are easily
implemented in APA type adapters but can be comparatively slow.

      The popularity of APA display adapter designs is increasing due
to its flexibility and the ease with which it can display
proportionally spaced characters.  The advent of VRAM technology has
allowed the rather slow process of forming characters pel by pel in
an APA refresh buffer to be done in a leisurely fashion by an MPU,
and still drive high resolution monitors.  Unfortunately, the time it
takes to completely update the refresh buffer with new characters can
be noticeably slower as compared to the older hardware character
generator designs.

      With the advent of higher performance processors this has
become less of a problem.  However, a dedicated A/N (alpha-numeric)
hardware processor can relieve the main display processor of all A/N
tasks, such as character generation, window/viewport movement,
resizing, data scrolling, etc.  Thus, the main processor can be
largely dedicated to the support of graphics/image operations while
the A/N operations run at full speed.

      An overview of the New Structure Display Adapter (NSDA) follows
after this paragraph.  There are many more novel features in this
design than doing fast proportionally spaced characters.  Although
the NSDA design illustrates a rich set of functions, a simpler subset
can be chosen as appropriate for a given design case.

      This adapter combines the best features of an APA-based design
and the more traditional character generator approach.  The result is
an adapter with flexibility for proportional spacing and composite
(graphics, image, and A/N) documents, but with the performance
typical of A/N only designs.

      The adapter supports many advanced features:
           Screen sizes up to 1 megapel, at video rates up to
           80 mHZ.
       .   Vector to Raster hardware graphics assist,
          optimized for GOCA requirements.
           Up to 14 proportionally spaced character fonts,
          concurrently, of 16 x 32 box size.
       .   16 colors out of a palette of 256k.
           Three programmable hardware viewports.
       .   Horizontal and vertical smooth scrolling.
       .   Advanced Attributing, including:
                Transparency
           -    Super and Sub Script...