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Character Displays Using Dot Matrices

IP.com Disclosure Number: IPCOM000087792D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Dyche, MP: AUTHOR

Abstract

Character display apparatus, such as the IBM 3277 display terminal, display characters formed from a dot matrix, for example 7 columns by 9 rows. Characters which can be displayed are stored in a read-only store. If the character can occupy the full 9 rows, then each character requires 9 words, each 8 bits long, within the read-only store. Thus a character set of 128 characters requires a read-only store of 128 X 9 = 1,152 words.

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Character Displays Using Dot Matrices

Character display apparatus, such as the IBM 3277 display terminal, display characters formed from a dot matrix, for example 7 columns by 9 rows. Characters which can be displayed are stored in a read-only store. If the character can occupy the full 9 rows, then each character requires 9 words, each 8 bits long, within the read-only store. Thus a character set of 128 characters requires a read-only store of 128 X 9 = 1,152 words.

The size of the read-only store can be reduced if the character set is designed so that only 7 rows can be used by any one character. If all of the upper case characters and those lower case characters such as b, d, f, h, k, 1, and t are arranged to occupy the top 7 rows, the lower 7 rows can be reserved for lower case characters such as g, j, p, q, and y. The other lower case characters would occupy lines 3 to 7 and thus no character would occupy more than seven rows of the dot matrix. By using a spare bit in each word in the read-only store, an indication can be given as to which of the two rows (the top pair or the lower pair) are to be used. Thus the number of words required in the read-only store to define each character can be reduced to seven or eight which is a convenient number for a read-only store module.

The idea can be applied to give a more flexible use of words within the read- only store module. Typically, the module may consist of 1024 words, each of 18 bits. Each display line of the...