I just picked up Don Lancaster's "TV Typewriter Cookbook".

It's pretty interesting, but I have some questions.

Do horizontal blanking lines contain sync pulses? Or are they just 63.5 microseconds of blanking level with nothing else?

If they contain sync pulses, then how long after a vertical sync pulse do I have to wait to send the horizontal sync pulse?

 

Hello,

Have a look at this:


This is one of the "slides" from this page:
http://www.ntsc-tv.com/ntsc-index-02.htm

Bertus

 

Hi bertus,

Thanks for looking that up. I do have that horizontal line timing diagram in my notes, but it still leaves me unclear about my questions above.

In Don's book, he says you should "allow 4 horizontal lines or more after vertical sync before displaying characters [or graphics]". Explaining that, "Several blanked horizontal lines should be provided following the vertical sync pulse. This gives the TV set a chance to catch up and adjust for the several horizontal sync pulses it may have missed during the vertical inverval."

So, given the purpose of the horizontal blanking lines, I'm unsure if they should have sync pulses or not. If the TV set has to catch up on missed H syncs, then I could see a reason for the H blanking lines not having sync pulses.

And there doesn't seem to be any mention (yet) of when to send the H sync after the V sync. The V sync pulse width (400 us) is already several times longer than one H line.

(I'm doing non-interlaced frames, by the way.)

 

You should send a horizontal sync pulse for the first horizontal line, immediately after the vertical sync.
There is no reason to not send a sync pulse with the horizontal blanking lines.
To "catch up" requires sync pulses, otherwise the horizontal oscillator is just oscillating at its free-run frequency (which is slower than the sync frequency).

 

Thanks guys.

 

Hello,

The blank lines are shown in this timeframe from the same page:


Bertus

 

Note that the double frequency horizontal sync pulses during the equalizing and vertical sync pulse typically keep the horizontal oscillator in sync.
It syncs on every other pulse during that interval.

 

Is that just for interlacing? The image Bertus linked to has a lot of interlacing information.

 

Hello,

You may have noticed the half lines in the even frames.
In the raster they show also:


Bertus

 

Is that just for interlacing? The image Bertus linked to has a lot of interlacing information.

Is what "just for interlacing"?
The double frequency sync before and after the vertical sync?

 

Is what "just for interlacing"?
The double frequency sync before and after the vertical sync?

Yes.

 

To make life easier, you want to ignore the 1/2 lines when your trying to display text the "EASY WAY", The easy way also means non-interlaced.

NTSC was once 60 Hz vertical which was sync'ed to the power line frequency. It, and the Horizontal frequency are now based on the color burst signal.

https://en.wikipedia.org/wiki/NTSC

When a transmitter broadcasts an NTSC signal, it amplitude-modulates a radio-frequency carrier with the NTSC signal just described, while it frequency-modulates a carrier 4.5 MHz higher with the audio signal. If non-linear distortion happens to the broadcast signal, the 3.579545 MHz color carrier may beat with the sound carrier to produce a dot pattern on the screen. To make the resulting pattern less noticeable, designers adjusted the original 15,750 Hz scanline rate down by a factor of 1.001 (0.1%) to match the audio carrier frequency divided by the factor 286, resulting in a field rate of approximately 59.94 Hz. This adjustment ensures that the sums and differences of the sound carrier and the color subcarrier and their multiples (i.e., the intermodulation products of the two carriers) are not exact multiples of the frame rate, which is the necessary condition for the dots to remain stationary on the screen, making them most noticeable.

 

I just picked up Don Lancaster's "TV Typewriter Cookbook".

It's pretty interesting, but I have some questions.

Do horizontal blanking lines contain sync pulses? Or are they just 63.5 microseconds of blanking level with nothing else?

If they contain sync pulses, then how long after a vertical sync pulse do I have to wait to send the horizontal sync pulse?

The vertical sync signal is "serrated" and contains BOTH the horizontal and vertical timing information. The leading and lagging duty cycles of the vertical sync also determine if an even or an odd field will commence. There's a LOT of information embedded in the vertical sync pulse!

 

What are you actually attempting to do?
You only need to know NTSC if you are going to generate composite video.
If you are trying to drive a computer monitor all you need is VSYNC, HSYNC and video or RGB.

 

What is amazing to me, is that they were able to generate this complex digital sync signal way back in the late 1940's with only vacuum tubes.
I believe it took about a 6 foot equipment rack of tubes to do it.
I imagine keeping that running was a major concern in the TV studio. Likely they had a least one backup on hand that they could rapidly switch to in case of a tube failure.
Fortunately the TV receiver could readily decode the sync using much simpler (mostly analog) circuits.

 

What are you actually attempting to do?
You only need to know NTSC if you are going to generate composite video.

Yes, just NTSC for now. It's more of a "something to do" project. Maybe make a simple video game. And eventually add some data to the signal from my DVD player. That's later down the line.

I'm thinking I need a cheap analog TV to practice with first; I don't want to break my [only] LCD TV.

 

Hello,

The following pages might interest you:
http://www.rickard.gunee.com/projects/video/pic/howto.php
https://courses.cit.cornell.edu/ee476/FinalProjects/s2004/dc248/dc248amz8/photos.html

Bertus

 

I'll check them out. Thanks.

 

Hello,

The following pages might interest you:
http://www.rickard.gunee.com/projects/video/pic/howto.php
https://courses.cit.cornell.edu/ee476/FinalProjects/s2004/dc248/dc248amz8/photos.html

Bertus

Also look at this:
http://www.brouhaha.com/~eric/ubicom/servid/