Sync on Lumanance [Y]

[JohnT]

Hi,

Is it possible to get composite sync under the lumanance channel [Y]?
I know about using the VBS signal for an external sync, but I like to use this output for my TV instead as an ext sync for my beamer.

Thanks, JohnT

[Barf]

The Y signal contains sync signals. (What is "composite sync"?) You can for example simultaneously get composite from the VCR-Scart, and Y from the TV-Scart (set the dBox to S-Video).

Barf

[JohnT]

Hi Barf,

Your right if you work with Y+C out.
The Y-signal is then on the CVBS (FBAS) ouput and the Chromanance on the Red output of the SCART.
But if you want to use a 'real' component output in YUV the Y-signaal doesn't carry any sync's.

btw: composite sync's are both Horizontal- and Vertical sync's combined in a sort of an /EXOR fashion where the negative slope is active.

Cheers, John

[Testbild]

Hi John,

use hardware

Feed the CVBS signal to an LM1881 (National) and get the TTL sync from that circuit. A slight disadvantage of this solution is a small delay caused by the RC low pass at the input, but I think the beamer can compensate it.

Regards

[JohnT]

@Testbild,

Yep, I know, respect!

I was hoping on a more slik solution like a small firmware change for the video decoder, but I don't know if it's capable of doing so.
Because that way can I route this DBox the same as I route the other equipment (like DVD and BetaCam) without switching over sync references or re-aligning video phases to compensate for the propegation delay of the LM1881 sync. sepertator.
btw; the LM1881 is an old type, there is a newer version which has a beter stability and doesn't need the RC filter on the input.
But I can't remember its name

How does the Dreambox do it?
Do they have sync on Y (like sync on green)?

Cheers,
John

[Testbild]

Hi John,

do you mean the Intersil EL4581/4583 Sync Separator? Seems to be a nice IC but I think it's hard to get.

To your other question: Yes, the Dreambox provides the luminance signal with composite sync in YCbCr mode (measured on Scart RGB).

Regards

[JohnT]

@testbild

Yep , that's the one, in particular the EL4581 that is pin compatible with the LM1881.

I just downloaded the datasheet of the SAA7126H and STV6412 (video encoder and the analogue SCART interface) to have a closer look on the possibilities of having sync on Y.

If there is anyone out there that all ready went through this please share the experiences.

Again, my goal is to get a proper and complete analogue component YCbCr straight out of this box to prevent timings errors.

references;
http://www.intersil.com/data/fn/fn7172.pdf
http://www.semiconductors.philips.com/a ... 127H_2.pdf
http://eu.st.com/stonline/books/pdf/docs/9754.pdf

JohnT