Apparatus and method for detecting an optical CRT display connected to a computer system
AssigneeKabushiki Kaisha Toshiba
InventorAkihisa Fujimoto
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Abstract
An optional display detecting apparatus is used in a computer system which has a flat panel display serving as a standard display unit and allows a CRT display serving as an optional display unit to be connected thereto. The apparatus includes a data replacing circuit for selecting a predetermined one of color registers in a digital-to-analog converter (DAC) and replacing color data stored in the selected color register with the test color data upon power-on of the computer system, and a voltage detector for comparing voltage levels at output terminals of the DAC with a reference level to determine whether the CRT display is connected thereto. A display controller drives a display unit selected according to comparison result from the voltage detector.
Claims21
An optional display detecting apparatus for use in a computer system which has a flat panel display serving as a standard display unit and allows a CRT display serving as an optional display unit to be connected thereto, comprising:
- display control means, having a plurality of color registers each storing color data, for designating an address to select one of the color registers, and converting color data stored in the selected color register into analog voltages to be output from output terminals as color component signals;
- data replacing means for selecting a predetermined one of said color registers, and replacing color data stored in the selected color register with test color data for testing optional display unit connection;
- and
- determining means for determining whether the optional display unit is connected to the output terminals obtained as a result of the conversion on the test color data set in the selected color register by said data replacing means.
A display controller for use in a computer system, comprising:
- video data generating means for generating a series of pixel video data along with at least synchronizing signals;
- digital/analog converting means, having a plurality of color registers each storing color data and output terminals to which an optional display is selectively connected, for converting color data stored in a color register corresponding to the pixel video data into analog voltages to be output from the output terminals as color component signals;
- register selecting means for selecting a predetermined one of said color registers;
- means for saving color data from and setting test color data for testing display connection in the predetermined color register selected by said register selecting means;
- and
- determining means for determining whether an optional display is connected to the output terminals, on the basis of voltage levels at the output terminals obtained as a result of the conversion on the test color data set in the predetermined color register selected by said register selecting means.
An optional display detecting method for use in a computer system which selectively converts color data stored in a plurality of color registers into analog voltages to be output from output terminals as color component signals, comprising steps of:
- selecting a predetermined one of said color registers;
- replacing color data stored in the predetermined color register selected in said selecting step with test color data for testing display connection;
- and
- determining whether an optional display is connected to the output terminals, on the basis of voltage levels at the output terminals obtained as a result of the conversion of the test color data stored in the predetermined color register selected in said selecting step,
- wherein said selecting step includes a step of selecting said predetermined color register upon start of power supply to said computer system, and said replacing step includes a step of saving color data from said predetermined color register selected in said selecting step and a step of setting test color data in said predetermined color register selected in said selecting step after said saving step.
Dependencies are inferred from the claim text.