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Font Organization for Multiple Performance Configurations

IP.com Disclosure Number: IPCOM000039805D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 5 page(s) / 78K

Publishing Venue

IBM

Related People

Finlay, DE: AUTHOR [+3]

Abstract

This article describes a baseline character generator that can be used to generate a raster image of a page from a memory that contains a coded and ordered representation of the page. More specifically, it describes a baseline character generator which has two performance configurations. The slower print speed configuration allows logic to be deleted without redesigning several pieces of the logic. The system shown in Figs. 1 and 2 provides for either a one-scan or a two-scan configuration for the font, font aligner logic, and the font address generation logic. Basically, the two-scan configuration processes two parallel scans of pel data at one time by duplicating the font data aligner logic and the scan buffer memories, and by reading the font data twice as wide per fetch (i.e., addressing cycle).

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Font Organization for Multiple Performance Configurations

This article describes a baseline character generator that can be used to generate a raster image of a page from a memory that contains a coded and ordered representation of the page. More specifically, it describes a baseline character generator which has two performance configurations. The slower print speed configuration allows logic to be deleted without redesigning several pieces of the logic. The system shown in Figs. 1 and 2 provides for either a one-scan or a two-scan configuration for the font, font aligner logic, and the font address generation logic. Basically, the two-scan configuration processes two parallel scans of pel data at one time by duplicating the font data aligner logic and the scan buffer memories, and by reading the font data twice as wide per fetch (i.e., addressing cycle). The font address generation logic generates font addresses in the appropriate order depending on the configuration of cards which are populated. A signal "onescan*" is generated on the font and scan buffer cards by the wiring on the card(s). The signal is readable by the processor and is used to control the font address generation logic. The character generator can print in 8 scan orientations, as shown in Figs. 3 and 4. The case numbers which are shown in the figure relate character orientation to scan direction orientation. For a machine with a fixed scan direction in relation to the long edge of the paper, the case numbers relate character orientation to paper orientation. If the machine feeds paper in two orientations as some printers do, the case numbers relate character orientation to paper orientation by the two separate but related methods. The case numbers are shown in parentheses in Fig. 3, and the binary representations used in the print I/O command are shown in quotes. The following is an overview of the character generator operation. The character generator consists of 4 memories which are addressable by the control unit: Font

Address & Escapement (A/E)

Page Buffer (PB)

Column Position & Escapement (CPE) Font Memory The font memory contains the raster dot (pel) patterns of all printable characters with one bit of storage for each dot or pel. A logical "1" appears as a dark pel. The control unit can read and write this memory as halfwords (16 bits) or as bytes. Address and Escapement Memory The address and escapement memory is a pointer table consisting of one entry for every character code (256) of every font (16) that can be printed. Each entry specifies the size of the character (height and width) and the address in the font where the character starts. There are two sets of these tables (normal and rotated), so there are a total of 8K (8192) entries (32K bytes). Only 254 character codes can be printed per font if 2 system codes are used as an end-of-line (EOL) and an end-of-page (EOP) character. (This is assuming an EOL and EOP code is in each font, which is not n...