What is a Scan Divider?
For the special case of converting from VGA at 640×480 (31.4 kHz H, 60 Hz V) to NTSC or SVGA at 800×600 (31.4 kHz H, 50 Hz V) to PAL, something simpler than a full blown scan converter may be satisfactory. In this case, it is only necessary to provide storage for a single scan line (rather than an entire frame store) since the input horizontal frequency is (almost) exactly twice that of NTSC (15.734 kHz) or PAL (15.625 kHz). A double buffer where one buffer is storing while the other is reading out at approximately half the VGA pixel rate should work. With appropriate timing, even lines become the even field and odd lines become the odd field (I may have this backwards). It is still not a trivial undertaking. Keep in mind that the quality you will get on NTSC or PAL will be poorer than the VGA due to fundamental NTSC or PAL bandwidth limitations. Also, flicker for line graphics will be significant due to the interlacing at 30 Hz. RGB to PAL Converter Chips (From: Gary L. Sanders (75052
