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Browse Prior Art Database

Randomized Refresh of Electrochromic Matrix Displays

IP.com Disclosure Number: IPCOM000043222D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 4 page(s) / 49K

Publishing Venue

IBM

Related People

Bird, CL: AUTHOR [+3]

Abstract

Electrochromic display images persist for a relatively long time in the absence of applied signals but eventually fade over a time period of several minutes. Because of this fading and also because the written image, in certain types of system, becomes progressively more difficult to erase with time, it is necessary to refresh the image by erasing and rewriting. Both erasure and rewriting are relatively slow processes so that sequential refreshing would be quite apparent to the display user. Accordingly, the present article proposes that the image be refreshed progressively on a non-sequential or pseudo-random basis. The size of the unit being refreshed in each individual operation may range from a single picture element to a complete line.

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Randomized Refresh of Electrochromic Matrix Displays

Electrochromic display images persist for a relatively long time in the absence of applied signals but eventually fade over a time period of several minutes. Because of this fading and also because the written image, in certain types of system, becomes progressively more difficult to erase with time, it is necessary to refresh the image by erasing and rewriting. Both erasure and rewriting are relatively slow processes so that sequential refreshing would be quite apparent to the display user. Accordingly, the present article proposes that the image be refreshed progressively on a non-sequential or pseudo-random basis. The size of the unit being refreshed in each individual operation may range from a single picture element to a complete line. An overall system for controlling the writing, erasure and refreshing of an electrochromic (EC) matrix display is shown in Fig. 1. The display 10 is addressed by means of row and column shift registers 11 and 12. The display is written initially, one line at a time. The row lines to be written are selected by the progressive shifting of a bit through the row shift register 11. Binary data corresponding to the desired picture elements of each line to be displayed are shifted into the column shift register 12 in between the shift operations of the row shift register. The control of these shifting operations and the assembling of the data to be written is controlled by a microprocessor 20. The microprocessor communicates with a host system via parameter passing register 21, which buffers commands and responses, and via a multiplexer 22, which passes data. When text characters are to be written on the display, these are provided on the host bus and stored in coded form in refresh buffer 23. Each character is written on the display 10 as an 8 x 12-dot matrix of picture elements. To assemble the lines of picture element data for writing on the display, the microprocessor uses the character codes stored in buffer 23 to address a read-only memory (ROM) 24 in which the dot matrix patterns corresponding to each character are stored. The dot matrix pattern corresponding to the character is then stored in a random-access memory (RAM) 25 as twelve 8-bit bytes, each of which corresponds to a different slice of the character. The process is repeated until patterns corresponding to all the characters of a complete line have been stored. For a normal full-screen writing operation, the microprocessor sets the row shift register 11 to zero and then loads a 1 bit into the first stage of the register via serializer 26.

Timing is provided to the shift register by timer 27. The timing signals are derived in timer 27 from the output of an internal crystal oscillator in the microprocessor. To assemble the first line of column data the top slice of each of the stored character patterns is read out of RAM 25 as a string of 8-bit bytes. These are serialized by serialize...