Browse Prior Art Database

LCD Controller Having Digital Pll

IP.com Disclosure Number: IPCOM000035963D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Itoh, H: AUTHOR [+3]

Abstract

Disclosed is a LCD Controller which can make both the CRT and the LCD panel visible at the same time, and which is programmable to meet different frame frequencies or a different construction of the internal LCD driver for the LCD panel. There are many LCD panels with different specifications. This invention makes the LCD control-clock asynchronous with the CRT dot-clock to be available to display both the CRT and each type of LCD at the same time. By using this approach, the programmable LCD frame frequency is available for gray- scale display with variable frame omission. (Image Omitted)

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 55% of the total text.

Page 1 of 3

LCD Controller Having Digital Pll

Disclosed is a LCD Controller which can make both the CRT and the LCD panel visible at the same time, and which is programmable to meet different frame frequencies or a different construction of the internal LCD driver for the LCD panel. There are many LCD panels with different specifications. This invention makes the LCD control-clock asynchronous with the CRT dot-clock to be available to display both the CRT and each type of LCD at the same time. By using this approach, the programmable LCD frame frequency is available for gray- scale display with variable frame omission.

(Image Omitted)

Fig. 1 shows an example of a system using this LCD Controller and CRTC (CRT Controller), DAC (Digital-to-Analog Converter), CRT, Buffer RAM, and LCD panel.

In general, the required timing of the LCD is shown in Fig. 2 and the required timing of the CRT is in Fig. 3.

Referring to Fig. 3, NO VIDEO area (Border area) is removed by the BLANK signal on the CRT. The number of Lines and Dots, the frequency of VSYNC and Dots which are output of the CRTC are different in each VIDEO MODE. On the contrary, as in Fig. 2, the number of Lines, frequency of HSYNC, VSYNC of LCD are required to be fixed for any LCD panels. In order to make the LCD panel visible, if the parameter of CRTC or frequency of Dot clock of CRTC are changed, the video screen image on the CRT gets out of shape; finally, at the same time the CRT and LCD are not made visible.

Fig. 4 shows a block diagram of the LCD Controller's internal logic. The "Read/Writ...