Browse Prior Art Database

Update Control for a Low Speed Display

IP.com Disclosure Number: IPCOM000041416D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Minshull, JF: AUTHOR [+4]

Abstract

A normal CRT refresh system repetitively transfers decoded screen data from the screen buffer to the CRT screen. The screen buffer to screen transfer rate is typically between 30 and 60 frames per second depending on the persistence of the CRT phosphor and the acceptable flicker. The transfer from the screen buffer to the screen is repeated unconditionally, and alterations to the contents of the screen buffer appear on the CRT screen 1/30 to 1/60 of a second after the refresh buffer is altered. Thus, while application programs may insert their data into the screen buffer in a variety of sequences, the screen does not need update logic to reproduce the sequence of insertions because the screen update appears to the human eye to be instantaneous already.

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Update Control for a Low Speed Display

A normal CRT refresh system repetitively transfers decoded screen data from the screen buffer to the CRT screen. The screen buffer to screen transfer rate is typically between 30 and 60 frames per second depending on the persistence of the CRT phosphor and the acceptable flicker. The transfer from the screen buffer to the screen is repeated unconditionally, and alterations to the contents of the screen buffer appear on the CRT screen 1/30 to 1/60 of a second after the refresh buffer is altered. Thus, while application programs may insert their data into the screen buffer in a variety of sequences, the screen does not need update logic to reproduce the sequence of insertions because the screen update appears to the human eye to be instantaneous already. New display technologies, such as electrochromics, have significantly longer retention times than a CRT phosphor but have a slower update performance. The time to update a raster row on an electrochromics display can vary between 12 ms and 20 ms (2 ms write, 10 ms to 18 ms erase approximately) whereas the refresh need only occur at intervals of a few seconds. The update rates to the screen buffer are determined by the application and will often be faster than the update capability of the display technology. Thus for the slower display technologies the transfer from the screen buffer to the screen must be selective to avoid any time wasted by the unnecessary transfer of data. The screen can then be made to mirror the state of the screen buffer more efficiently than for a CRT and also to reflect the update order of the screen buffer data. An attachment method for an electrochromic display uses an IBM Personal Computer where applications executing in the Personal Computer generate display data which is inserted into the refresh buffer of the display adapter for transfer to the electrochromics display. The mechanisms to manage the refresh buffer to screen update are provided by a screen manager running on a microprocessor in the Display Adapter, shown in Fig. 1. To achieve an ordered and efficient update of the electrochromics screen 1, it is necessary to implement a flagging system which indicates which locations in the refresh buffer 2 have been updated. The application screen interface 3 marks the locations in the refresh buffer which contain changed display data by setting flag bits in a flag register 4. Each unit area of the screen is allocated a bit in the flag register. The screen buffer to screen transfer logic 5 monitors the state of the flag register bits and transfers to the screen the contents of screen buffer locations for which flags are set. Before the start of the transfer for a particular flag the flag is reset by the transfer logic. In this way only the locations in the screen buffer which are updated are copied to the screen. The granularity of the flagging may vary. In the present implementation a flag bit per character row of t...