Fluorescent backlight flicker control in an LCD display

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a circuit for controlling the frequency of the fluorescent backlight used in a dual layer supertwist LCD, such as described in detail in the December 1988 issue of Byte Magazine, pages 321-324, hereby incorporated by reference.
The backlit LCD is provided with a compensator to produce a page white display, similar to a typewritten page having a white background with black or grey characters.
The backlight comprises a pair of 2.
5 watt fluorescent bulbs.
The fluorescent backlit dual supertwist LCD is provided with Zenith Data Systems TurbosPort 386 portable personal computer.
The TurbosPort 386 portable personal computer is driven by an Intel 80386 32 bit microprocessor.
A CMOS version of the Intel 80386 microprocessor is utilized to reduce battery power consumption.
The CMOS version 80386 operates at 12 MHz and is switchable down to 6 MHz to conserve battery power consumption.
The machine features zero wait state technology which obviates the need for the microprocessor to slow down to wait for slower components to catch up.
This allows the machine to run faster than models with higher clock speeds that have to wait.
The principles of the invention are applicable to various LCD display controllers.
For example, the LCD display may be driven by an LCD display controller 15, such as a Chips and Technologies model 82C455 or as Cirrus model chip set CL-GD610/620.
These LCD controllers 15 provide a horizontal sync signal HSY; a vertical sync signal VSY, a dot clock signal, eight data signals and a signal to prevent AC bias on the LCD.
The latter signal is sometimes provided within the LCD.
With such LCDs, it is unnecessary for the LCD controller to provide such a signal.
The horizontal sync HSY and vertical sync VSY signals control the application of the voltage to the electrode matrix in the LCD.
The system is set up such that eight parallel bits of data are written to the LCD at a time under control of the dot clock.
The first 4 bits are written to the first 4 pixels located at the upper left side of the first line of the display