Browse Prior Art Database

Conversion of CRT Character Position to Buffer Storage Address

IP.com Disclosure Number: IPCOM000083252D
Original Publication Date: 1975-Apr-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

McGriff, FE: AUTHOR

Abstract

In information display systems using a cathode-ray tube (CRT) for the display, it is desirable to have an easily determined relationship between the position of a character space on the tube face and an address in a buffer storing the data to be displayed.

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Conversion of CRT Character Position to Buffer Storage Address

In information display systems using a cathode-ray tube (CRT) for the display, it is desirable to have an easily determined relationship between the position of a character space on the tube face and an address in a buffer storing the data to be displayed.

In a recently developed information display system, each display station contains a buffer which is used for preparing and storing data that is displayed on the screen. There is a fixed relationship between each buffer storage location and its character position on the display screen. This relationship is defined by a table in which there is a one-to-one relationship between a display position and a storage address, but the relationship is not a simple one.

The algorithm presented defines the relationship between a CRT screen position and its corresponding buffer location, in terms of arithmetic and logical operations on the EBCDIC bit pattern of the position value. Thus, this algorithm represents a rule form, rather than an enumeration form of the function which maps a row-column screen position value into a buffer address.

The algorithm performs the position to address conversion in four phases: Phase 1. Linearization of the row-column position value of the character. Phase
2. Forming a pseudo-row buffer address. Phase 3. Forming a pseudo-column buffer address. Phase 4. Handling exceptional cases. The algorithm is defined as an APL/360 dyadic function identified here as MAP3270. Line 3 of the function transforms the two-dimensional specificati...