Compaq Computer Corporation, Inc.

Daniel B Reents

Patrick R Cooper

Randall L Hess

Hung Q Le

Gaines C Teague

Philip James McKenzie

James H Garrett

A liquid crystal display (LCD) panel which has its contrast controlled through the use of a pulse width modulation (PWM) circuit contained in the video controller and a contrast control circuit. In response to a particular video refresh mode, the PWM circuit modulates the pulse width of a signal that is an input to the contrast control circuit. The pulse width is changed by the use of a base contrast register and two offset registers. Depending on the video mode, the base register is used alone or is combined with one of the offset registers to provide a signal to indicate the duty cycle of the signal. The pulse width modulated signal is converted to a DC bias contrast voltage which is provided to the LCD panel.

Circuit for controlling bias voltage used to regulate contrast in a

A computer system with a digitizer based screen display in which the digitizer data is buffered through a first-in first-out memory (FIFO). The processor is only interrupted when a full digitizer data packet is available in the FIFO, rather than being interrupted on each data byte available in the FIFO. The FIFO can hold multiple digitizer data packets, so that data is not lost should the processor in the computer system be unable to immediately handle these digitizer data packets. The system also provides a filter in a separate controller that examines each digitizer data packet to determine if the pen is in a predefined screen location that performs a prespecified function. If so, rather than pass the digitizer data packet to the system processor through the FIFO, the command is passed through a separate register to the processor based on the 'hotspot' touched on the screen.

Buffering digitizer data in a first-in first-out memory

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Spring, TX, United States of America

Daniel B Reents