[Openchrome-users] only NTSC modes in VT1626 TV-out modes? -> need PAL

[Lloyd Williams]

On Saturday 05 August 2006 13:45, John Robinson wrote:
>
> I'd quite like to try progressive not interlaced, but presumably it
> means a line rate of 31.25kHz, which would be WAY out of spec for my
> standard TV, so dangerous to even try?
>

The old Amigas and Playstations (and probably more besides) used to have a 
trick for this.

Normally the tracing of the second interlaced field is triggered by a vertical 
sync pulse during the *middle* of the last scanline of the first field. The 
tracing of the first scanline of the second field then begins in the middle 
of the screen (just above the middle of the first scanline of the first 
field).

If you remove this half-scanline offset (by using an even number of scanlines 
per frame and hence per field) then the CRT traces the second field straight 
on top of the first field, effectively giving you 288p at 50 Hz (PAL) or 240p 
at 60 Hz (NTSC).

I have done this before with XFree86, a VGA-to-SCART converter and an old VGA 
card, though I don't have the modeline handy. It might not be possible to do 
with the Via TV encoders. Will someone more familiar with them please inform 
us?