Greetings guys... Happy Holidays...

Can anyone describe or show me what the vertical sync signal should look like for NTSC Non-Interlace Progressive display, please?

TIA... Cheerful regards, Mike, K8LH

Hi Mike,

NTSC is a television standard whose specification includes interlacing in its definition, so it's contradictory to speak of a non-interlaced NTSC signal. However, most televisions and video monitors intended for use with NTSC can successfully display a non-interlaced signal such as that produced by some microcomputers. Homebrew microcomputer builders sometimes prefer the slightly simpler timing requirements when interlacing is omitted. But this option is somewhat of a tradeoff for reasons I won't go into now.

What is it that prompts your interest in the subject? It would be easier to direct you to useful information if we knew what goals you had in mind.

-- Jeff

P.S. - perhaps you're not serious, and the goal is to supply us with some holiday humor!

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Hi Jeff and gang:

I'd like to generate a composite video signal stream to display 40x25 text on an NTSC compatible display, much like Daryl and Grant do with their AVR designs, but I'd like to use a PIC instead of an AVR. The PIC is clocked at 64-MHz which provides performance very similar to that of the 16-MHz AVR chips in Daryl's and Grant's designs. That is, I will have 1016 PIC instruction cycles to work with (Tcy = 62.5-ns) during each 63.5-us horizontal scan line, just like the AVR chips.

I've peeked at Daryl's and Grant's code but I'm struggling with AVR assembly language. Daryl was kind enough to reply to an email and, if I understand correctly, he's using a simplified vertical sync method that generates three lines with a 990 cycle (61.875-us) sync pulse at the beginning of each 262 line "frame" and an 80 cycle (5.0-us) horizontal sync pulse at the beginning of all the remaining lines in each frame.

Thanks for all the help, guys...

Happy Holidays. Cheerful regards, Mike


My request was serious and sincere. I apologize if it seems otherwise.

LOL! Hi, Mike. The joke is on me! It'd be very easy to pull my leg, simply because I'm so earnest when faced with a technical problem.Each 262 line field. With interlacing it takes two fields to equal a frame. NTSC transmits the 262 odd-numbered scan lines (comprising one field), followed by a V-sync pulse, then the 262 even-numbered scan lines (comprising another field, and followed by another V-sync pulse); then the process repeats. NTSC carries roughly 60 fields, ie 30 frames, per second. Interlacing tends to reduce flicker (compared to a non-interlaced display running at the same frame rate).

Of course it's undesirable that the odd & even lines should appear in exactly the same place on screen. What you want is for the two fields to be slightly displaced from one another vertically so the odd & even lines appear intermeshed ("interlaced") as you'd expect. To accomplish this, 1/2 line is added to each field, for a total of 262.5 lines per field (525 lines per frame).

The half-lines aren't visible, as they occur during vertical retrace. Their purpose is merely to waste a bit of time. During this time the television/monitor's vertical sweep oscillator -- which runs at a steady rate -- will have advanced slightly in its cycle, which is just what's required for the slight vertical displacement I mentioned. This takes some thinking about, but makes sense. With 525 lines per frame, the hor. & vert. oscillators can run at a steady rate, the lines intermesh properly, you chop in half a line you can't see anyway, and it all works out.

The good news is, CRT-type TVs and monitors are very tolerant of non-standard frequencies. You are not obliged to exactly match the specification for scan rates -- you can count on at least 5% tolerance, and typically much more, depending on the TV. (I expect LCD monitors also have a degree of tolerance, although perhaps not as much.) So, re scan frequencies, don't worry too much about the numbers after the decimal point. Where exactness is vitally important is in consistency of timing. Otherwise the display on-screen will appear "torn".

The bad news is, it feels like I'm not explaining this very well. But there's lots of reference material available, such as the Wikipedia article on NTSC, and other sources, I'm sure. Keep us posted on your progress!

cheers,
Jeff

_________________
In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Have you consulted the Commodore 64 Reference Guide? It has some information so you might be able to figure the rest out or partly guess what it would look like.

I haven't looked at that one, yet. Thanks for the tip.

Daryl was kind enough to share some info' on his 40x25 non-interlaced display and I have another couple examples of interlaced displays so I'm ready to start coding and experimenting. Ultimately, I'd like to duplicate the functionality of Daryl's 40x25 display using a 20-pin PIC running at 32-MHz...

Cheerful regards, Mike