NTSC/PAL signals

[dknguyen]

It seems I don't know what term to Google in order to find information on how an NTSC or PAL signal works.

I'm thinking of trying a video overlay project, and I'm pretty sure it's futile to do everything from a microcontroller without a video overlay ASIC (or a Parallax Propeller which seems to have that stuff built-in). But I'd still like to know what's going on.

EDIT: Yup, everyone seems to either use an ASIC or design one from scratch and implement it in an FPGA or DSPs...whew, that's daunting.

 

[mneary]

You want something like "NTSC timing specifications"? Wikipedia has a pretty thorough article although somebody has questioned it.

I found some clever scheme from an old computer that made a crude NTSC or PAL with the Z80 CPU with the search terms "sinclair zx81 timing".

Now it shouldn't be quite as difficult with micros having sub-microsecond instruction cycles!

 

[Nigel Goodwin]

Why not use an OSD chip?, easy to use if you can find the datasheet for them (I used an NEC one years back as the datasheet was available).

 

[MrAl]

Hi,


I just thought i would mention that screen displays made on the regular
TV display never looked that good. Maybe on HD TV or something might
be better though. The displays that show up on normal TV's are pretty
resolution limited, unless you dont need much.

 

[fernando_g]

I agree with Nigel, an OSD chip is the easiest path to go.
I used a Sanyo device many moons ago, worked very well.

PAL and NTSC are quite similar in essence, they differ in the vertical and horizontal sync timing, the chroma subcarrier frequencies and the fact that PAL alternates the chroma subcarrier phase each line (thus the name). There are other more subtle parameters, like the infamous NTSC black setup. SECAM is a totally different beast altogether.

However, with the OSD chips, they take care of all those issues, all you need to do, is to feed them the text overlay you want to display serially from your microprocessor. A video buffer will also be required at the output if you have to drive 75 ohm loads.

 

[dknguyen]

Why not use an OSD chip?, easy to use if you can find the datasheet for them (I used an NEC one years back as the datasheet was available).

Please reread the second part of my OP. I don't have any intention to do the overlay part from scratch, but I'm not the kind of perosn who likes coding for RS-232, SPI, or I2C blindly in software without having any idea of what is physically going on.

It looks like it might be massive PITA to make something like an line that has to rotate on the screen though because, for the most part, it seems things like the MAX7456 were made to display text charagers. And piecing together a rotating line means lots of special characters for lines of different angles pieced togethered just right.

 

[fernando_g]

Then the best book for what you are looking may be "Video Demystified: A Handbook for the Digital Engineer" by Keith Jack.

 

[blueroomelectronics]

This may do what you want.
**broken link removed**

 

[dknguyen]

Yeah, I'm leaning more towards that because it has vector graphics. THe downside though is that it's bigger, if only for the reason that I need to connect my own board onto it. THere's also the fact that it needs 5V instead of 3.3V. But other OSD ICs need that too, as do many inertial sensors.