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Incremental Erasing in an Electrochromic Display Device

IP.com Disclosure Number: IPCOM000041417D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Minshull, JF: AUTHOR [+3]

Abstract

An electrochromic display device can be attached to a processor, such as the IBM Personal Computer. The display technology is such that pels (picture elements) are written by selecting a horizontal row and applying an electric charge to selected vertical columns for about 2 milliseconds. Pels are erased either by selecting a single horizontal row and grounding selected vertical columns for about 20 milliseconds, or by selecting a number of horizontal rows simultaneously and grounding all the vertical columns for a variable period which ranges from 20 msecs for two rows up to 200 msecs for over a hundred rows. The fact that erase time is less than linearly dependent on the number of rows being erased means that the system designer has a choice of two ways in which to update an alphanumeric display on an electrochromic screen.

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Incremental Erasing in an Electrochromic Display Device

An electrochromic display device can be attached to a processor, such as the IBM Personal Computer. The display technology is such that pels (picture elements) are written by selecting a horizontal row and applying an electric charge to selected vertical columns for about 2 milliseconds. Pels are erased either by selecting a single horizontal row and grounding selected vertical columns for about 20 milliseconds, or by selecting a number of horizontal rows simultaneously and grounding all the vertical columns for a variable period which ranges from 20 msecs for two rows up to 200 msecs for over a hundred rows. The fact that erase time is less than linearly dependent on the number of rows being erased means that the system designer has a choice of two ways in which to update an alphanumeric display on an electrochromic screen. Assume (for example) that characters are drawn in a box that is 12 pel rows in height, and that a typical row of alphanumeric data will require non-blank pels in 9 of those 12 pel rows: then, if only a single row of characters is to be updated, it will be possible to erase and write each pel slice of the character row serially in 9 x (20 +
2) = 198 msecs, and the visual effect will be that the old character content of the row will appear to merge imperceptibly into the new character content of the row without any intermediate period when the row is totally blank on the screen. However, if many character rows of the screen have to be updated, and a time lapse of 198 msecs per character row is felt to be excessive, then it is possible to erase (say) 10 character rows in parallel before writing them serially. The total elapsed time using a parallel erase strategy over 10 character rows will be 200 + (10 x 9 x 2) = 380 msecs, compared with 10 x 9 x (20 +2) = 1980 msecs using a serial erase strategy, but the visual effect of the parallel erase strategy includes a period when all 10 character rows are blank. Those who are familiar with slow- erase display technologies, such as electrochromics, will recognize that both update strategies have their place. However, when human factors are taken into account, serial interleaved erasing and writing seems to be preferable when a single character row is to be updated, or when two or more widely separated character rows are to be updated, but parallel erasing followed by serial writing is to be preferred when many adjacent character rows need to be updated at the same time. It is necessary then for an electrochromic display adapter to have some algorithm for deciding when to do serial interleaved erasing and writing, and when to do parallel erasing followed by serial writing. A convenient algorithm which has proved to be effective in practice is to review all of the rows needing to be updated, and if two or more non-blank rows which need to be updated are either adjacent or separated only by blank rows, then the set of ...