On 8/8/06, James Richard Tyrer <[EMAIL PROTECTED]> wrote:
Note that mode 1 only has 350 or 400 vertical lines in the VGA emulation modes and the default vertical is 70 Hz with 900 total lines. How would our TV out handle this? OTOH, real CGA character mode (which is in the IBM VGA spec) will work on a TV since it is non-interlaced with 200 visible lines and 262 total lines at vertical 60 Hz .
Keep in mind that we have a disconnect between what the host thinks VGA is doing and what we're actually scanning out of the video controller. The VGA emulator program converts continuously from one to the other. Thus, we can have any physical resolution that we want. For the TV, we configure the video controller appropriately and set up the converstion program to handle the appropriate size of the output framebuffer. Also, if you're wondering how to tell if there's a TV on there, you just don't need to. Head 0 has the analog DACs, useful for a multisync monitor. We'll configure that via DDC (typically). Head 1, IIRC, is connected to the TV chip. We'll just configure the TV according to the region (different BIOS images?) on head 2. Then we set up the two (independent) video controllers to scan out the same framebuffer at two different resolutions (one or both will use the INC instruction in the vc to skip the extra space), and viola!
Actually, TVs manufactures have found ways around this. The last Sony my family purchased some years ago claimed a horizontal resolution of over 1000 lines. At the time I thought this was odd since it was considerably more than the theoretical limit of +/- 360. IIUC, they achieve this by using a comb filter rather than a LP filter to remove the color subcarier from the luminance signal. If using the S-Video output, this wouldn't be an issue.
In my experience, s-video + comb filter is STILL awful. Hypothetically, this does a MUCH better job of isolating the chroma from luma. But the color resolution is STILL only about 160 viewable. If you had a B&W image, you'd think you'd see crisp lines at arbitrarily high horizontal resolutions. I just never have. It's like the TV is imposing a low-pass filter or some sort of blur or has really crappy analog circuitry. I'd love to see a TV that didn't do this. _______________________________________________ Open-graphics mailing list [email protected] http://lists.duskglow.com/mailman/listinfo/open-graphics List service provided by Duskglow Consulting, LLC (www.duskglow.com)
