cvt modeline generator

[Luc Verhaegen.]

On Sat, Jan 07, 2006 at 03:13:01PM +0100, Nicolas Mailhot wrote:
> Hi,
> 
> I am wondering if the cvt modeline generator is still not slightly
> wrong.
> 
> I've just stumbled on page 55 of this manual :
> 
> http://support.nevt.co.jp/dl_service/data/user_manual/ENGLISH/HT1000/ht1000_e_4.pdf
> 
> which lists the standard frequencies and pixel clocks a video projector
> expects
> 
> For example for 750*576 at 50 (SDTV, basically the mode you find on PAL
> DVDs) this document states:
> hsync: 31,25 kHz, field rate: 50 Hz, pclk: 27 MHz
> 
> And the CVT generator will output:               
> hsync: 29.58 kHz, field rate: 49.62 Hz, pclk: 26.50 MHz
> 
> Which seems a lot less sane to me.
> 
> Am I missing something ?
> 
> -- 
> Nicolas Mailhot
The mode is 720x576 at 50Hz, 750 isn't rounded to 8.

CVT rounds the pixelclock down to 250kHz, as done in the CVTd6r1.xls.
A dotclock of 26.75 gives you 50.09Hz.

Also, this is CVT timing, not a pre-defined mode. For instance; CVT will 
generate modes with a VTotal of 596 while PAL would have a VTotal of 625.

You will not generate an exact PAL mode with gtf either.

Luc Verhaegen.