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Prefetch of Attribute Bytes in a Display Buffer

IP.com Disclosure Number: IPCOM000049020D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Emerson, GA: AUTHOR

Abstract

This article describes a method of detecting field attributes and extended field attributes in a mapped display buffer. Typical prior systems have 8-bit code bytes mapped in 16-bit pairs (e.g., 0,1) in the following manner: (0) Field Attribute-(1) Extended Field Attribute (2) Character -(3) Character Attribute (4) Character -(5) Character Attribute " " " " " " " " (N-1) " -(N) " (N+l)Field Attribute-(N+2) Extended Field Attribute (N+3)Character -(N+4) Character Attribute etc. etc.

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Prefetch of Attribute Bytes in a Display Buffer

This article describes a method of detecting field attributes and extended field attributes in a mapped display buffer. Typical prior systems have 8-bit code bytes mapped in 16-bit pairs (e.g., 0,1) in the following manner: (0) Field Attribute-(1) Extended Field Attribute

(2) Character -(3) Character Attribute

(4) Character -(5) Character Attribute

" "

" "

" "

" "

(N-1) " -(N) " (N+l)Field Attribute-(N+2)

Extended Field Attribute (N+3)Character -(N+4) Character Attribute

etc. etc.

In a typical system, Field Attributes (e.g., byte 0) have the code form 11XXXXXX and are recognized by the leading "11". Extended Field Attributes (e.g., byte 1) are recognized by the fact that they always follow the corresponding Field Attribute.

In a display using a one-byte wide memory output bus, it is advantageous to decode the Character Attribute before the corresponding Character. In this way, the display device can activate its attribute mechanism (e.g., highlighting) to be ready to show the Character code as soon as it is fetched. Thus, it would be advantageous to fetch the above-identified bytes in the following order: 1, 0, 3, 2, 5, 4. etc.

This creates a problem in detecting the Extended Field Attribute because it no longer follows the easily detected Field Attribute. One possible solution would be to save all data in the Extended Field or Character attribute position (e.g., byte
1), until the next data position (e.g., byte 0) is read and then determine whether or not...