Portable PC simultaneously displaying on a flat-panel display and on an external NTSC/PAL TV using line buffer with variable horizontal-line rate during vertical blanking period

摘要: A scan converter receives VGA or SVGA graphics data and outputs NTSC PAL TV data. The is integrated inside a personal computer's controller, allowing the digital-to-analog (DAC) to be used for either CRT-pixel conversion encoding. timing altered better match with scan-conversion. horizontal rate not constant but can increased decreased during vertical blanking period. second register provided total number of pixels in line blanking, while first contains displayable Since lines fewer require less time display, period blanked changed. An extra added every frame asymmetry standards. While CRT's cannot accept variable rate, flat-panel displays operate properly even when varies. Thus an image simultaneously displayed on both external portable display.