Browse Prior Art Database

Method to Operate Liquid Crystal Display in Monochrome or Color/ Graphics Adapter Modes

IP.com Disclosure Number: IPCOM000061332D
Original Publication Date: 1986-Jul-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Arismendi, A: AUTHOR [+2]

Abstract

A method is described to allow application programs which utilize the monochrome or color graphics adapter to drive their respective displays or a liquid crystal display. Both the IBM Monochrome Display Adapter and the IBM Color/Graphics Monitor Adapter utilize the Motorola 6845 CRT Controller module. Both adapters also format their respective displays as 25 lines of text with each line containing 80 characters. Only the color/graphics adapter displays graphics data. Substituting a liquid crystal display (LCD) for both monochrome and color/graphics displays for application program transportability requires the LCD Controller to allow I/O port and display memory address programmability. The monochrome and color/graphics adapter's respective I/O port and memory addresses are listed in the following table.

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Method to Operate Liquid Crystal Display in Monochrome or Color/ Graphics Adapter Modes

A method is described to allow application programs which utilize the monochrome or color graphics adapter to drive their respective displays or a liquid crystal display. Both the IBM Monochrome Display Adapter and the IBM Color/Graphics Monitor Adapter utilize the Motorola 6845 CRT Controller module. Both adapters also format their respective displays as 25 lines of text with each line containing 80 characters. Only the color/graphics adapter displays graphics data. Substituting a liquid crystal display (LCD) for both monochrome and color/graphics displays for application program transportability requires the LCD Controller to allow I/O port and display memory address programmability. The monochrome and color/graphics adapter's respective I/O port and memory addresses are listed in the following table.

(Image Omitted)

Table 1 shows that the I/O port addresses differ by only 2 bits and display memory addresses differ by 1 bit between the two adapters. The logic diagrams of Figs. 1 and 2 show how the LCD Controller is mapped between the two sets of display memory and I/O port addresses. Fig. 1 shows the generation of the I/O port address select but does not show the generation of all register selects using +A3 through +A0 due to their straightforwardness. Address bits above +A9 are not shown, and logic which detects when they are zeros is also straightforward. The generated select signal would have to be gated by I/O read or write cycle control lines to perform the appropriate function. Since 16K is needed for color/graphics operations, address bits +A13 through +A0 are passed directly to the display memory through the LCD Controller. Monochrome display application programs are designed to execute using 4K bytes of memory. There is no need to check that address bits +A13 and +A12 are zeros because of this monochrome display memory size restriction. The generated sele...