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Old 14th Jan 2011, 7:23 pm   #43
pitbuell94
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Join Date: May 2009
Location: Fresnes, France
Posts: 124
Default Re: 819 line standards convertor.

Hi Darryl and PPPPenguin,

Make this converter seems to be a nightmare .

In fact, the hard part with TDA8708, LM1881 and TDA8702 is not a big issue.

All the part are on a board but nothing run . (nothing burn too ).

The main and the big issue is the software to drive all the function.

Well, I need some information.

When I design my VHDL code, I suppose I build the design of the read part and write part as 2 single separate design part?

Only a signal coming from the write part give the information to the read part that there is some data ready to read.

In my design, after 2 lines comes, I want to start the read part.

Of course, I need to calculate the time needed to have good synchro signal between 819 and 625.

Let me explain my point of view :

Because I start to read 819 signal after 2 lines coming from 625 and because the video signal comes at line 23, I start to read line for 819 signal at the start of line 25.( I need a minimun of 2 lines to start my process...).

So, this time need 64Ás * 25 line => 1536 Ás.
The VBI for 819 is equal to 38 lines * 48,84 => 1855,92Ás.

Then, 1855,92 - 1536 => 319,92 Ás.

319, 92 Ás / 64 Ás => 4, 998 lines

So, the start of field one in 819 starts at the beginning of line 621 of 625 lines standart.

Is-this correct or do I drink too much ?

If I start my read process at line 621, in fact, I loose the first picture coming in the system, but normaly the rest of the process should be well synchronised, isn't it?

Have a good night.

Frederic Cabanes.
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