Realtime video

[RUBiksCUbe]

Ive been trying animated tv signals where the white bar moves back and forth, but it isnt working out. All I see is a white bar in the middle of the screen that gets warped at the top. I guess the vertical synch is important

[mytekcontrols]

Yes you will need Vsync, otherwise you'll get that bending affect you are seeing. Also be sure to leave some empty space (0.4 volt black level) of at least 3 scanlines before and after (more is better if it doesn't limit the viewable height of your bars). This is kinda like the front and back porch of the Vsync pulse.

Speaking of which, are your front and back porch adaquate for your Hsync? If you look at the diagram below you will see that you need to maintain at least 1.5 usec of space for the front porch, and about 4.7 usec on the backporch of the Hsync. To be safe, and because most TV's have considerable overscan, I would give it more (figure on only having about 48 usec of viewable active video, the rest just wraps around the CRT).

<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=627&stc=1&d=1132554180 ">

For now don't worry about the colorburst, since I presume you are only fooling around with B&W. Also if you didn't already notice, IRE units are the same as volts*100.

[RUBiksCUbe]

When I timed every section of my code in MPLAB I got it as close as the specifications as possible. The front porch was 1.4us and the back porch was 4.6us, which is as close as I could get it without going over. I could try to extend the front porch to 1.6 us and see what happens. I dont think that anything would though.

Thats a good diagram. I wish I had that when I was still coding. Do you have one of those for the vertical synch? I cant find the timing for it anywhere.

[mytekcontrols]

RUBiksCUbe:

Thats a good diagram. I wish I had that when I was still coding. Do you have one of those for the vertical synch? I cant find the timing for it anywhere.

Here's a link to where I got the Hsync diagram (they also have one for Vsync) http://www.sxlist.com/techref/io/video/ntsc.htm

You'll notice if you look at the FLD 4 example, that they show 6 equalizing pulses ocurring before and after the Vsync. Most modern TV's don't need these any more. This was originally used to help the older sets lock in properly, which is also why these sets had horizontal and vertical adjustments, something you also don't see any more. As for the Vsync pulse, instead of it being one long pulse, it is actually made up of both long and short pulses. Essentially it is just hsync turned upside down for 3 scan lines. Therefore the total length of the Vsync pulse is approximately 191 usec, and occurs approximately every 16 msec.

A good way to produce these signals is to use the PIC's internal counters in an interrupt routine. Or if you have an HPWM on board, you can also mimic these sync pulses by properly setting the duty cycle and base frequency (this is easily done via PBP).

Have fun,