analog video signals

Component video.

Microcontollers are too slow for such a task. Display controllers are a specfic kind of faily dumb (as a rule) processor of sorts.

As ever........ What is it you actually want to do ?????

Graham

There are a couple of projects on avrfreaks that use an AVR microcontroller and 2 outputs as a 2 bit dac to generate NTSC timing and video... puts 120 pix x 90 pix in B&W on a TV. If you told me you were trying to do that, I'd have bet against you ever getting it to work. I suppose I have to believe it... there was a picture of the screen... maybe it was all bogus?

Look on Amazon.com for "The Cheap Video Cookbook" by Donald E. Lancaster. There's a second book in the series also, "Son of Cheap video".

These may tell you more.

There are a lot of things that could qualify as "analog video," but the sort which most commonly are found going from a PC to its monitor (the "VGA" interface) are three separate signals (one each for red, green, and blue) which have an amplitude of

0.7V p-p, and in which the most positive excursion of the signal, with respect to the blanking level, is considered "white". (Note that you will often see the "white" level for each channel as 0.7V positive with respect to the video return pins, but technically VGA is an AC-coupled system and the white level is supposed to be referenced to the blanking level, not "ground.") Oh, and this assumes a 75 ohm termination impedance.

The vertical and horizontal sync signals are seperate, each on its own physical line, and are positive-true pulses at standard TTL levels.

A microcontroller by itself would likely not be fast enough to generate anything but the crudest video; for even the lowest standard format (640 x 480 at 60 Hz), you need a pixel rate of a bit over 25 MHz. Simple pattern generation (color bars, etc.) can often be done with just a microcontroller, though. Actually, I put together just such a generator a number of years back, for the purpose of EMI testing of monitors. What is it you're trying to do, exactly?

Bob M.

What rubbish I have designed microcontrollers into numerous video projects.

I have used PIC micros to do it. So long as you keep the timing tight it works fine.

Really? My monitor is 2048 * 1536 resolution. Lets see you drive THAT with a PIC. BTW, I want true color, not that 16 bit crap.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Right now, I just want to understand how it works a little better - I don't have a specific project.

BTW, if you spread out the horizontal retrace pulses, will this actually slow down the speed at which lines get updated? And, similarly, if you spread out the vertical syncs, will this slow down the speed at which it moves down a line? If so, I was thinking maybe you could send analog video to an LCD monitor with really spread out horizontal and vertical sync signals using a cheap microcontroller.

For instance, instead of doing 1 frame in 1/60 of a second, you might take a minute to draw the frame.

How fast is your bit clock ?

Graham

What "horizontal retrace pulses" ?

Do you make this stuff up as you go along ?

You have not been doing any thinking at all have you ?

What you should do is some *LEARNING* and stop wasting other ppls' time.

Graham

colloquially "VGA" technically it's "RGB" with separete sync signals RGB is a class of component video

I expect so, getting more than a blank screen or horizontal bars could be a challenge on the lesser micros, although even there it may be possible to do some trickery with a fast synchronous serial port and emit a monochrome image.... Bye. Jasen

[vga timing]

maybe.

LCD is more forgiving than cathode ray, if it has a video input that runs at the normal TV scan rates it can probably handle those rates on the VGA input too.

probably not. I doubt that the electronics inside the monitor is designed to go that slow.

Another option may be to interface your microcontroller with an old ISA bus VGA card... you won't need all 118 lines, just 17 address lines (16 if you don't need colour text mode) 8 data, and maybe 8 others. the card may need the -12V supply for the output to work. (I had one like that in a PC)

--

Bye.
   Jasen

That's it Donkey. Attack, rather than explain.

The proper term is "Horizontal Sync", and it can only be varied within the limits of the monitor you use. I have never seen a monitor that could take one minute for a single horizontal scan. It has to be real time, because the monitor needs all of the signals synchronized to create the image you want.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I never said it was for PC video.

One project was to use a PIC to drive an on screen display for a CCTV system. The PIC cut into the picture to display time and camera information.

Clearly for PC type resolution you need to go for a proper video card. Or use a PIC with some dedicated video hardware.

I wasn't assuming it was specifically but you'll have a bit clock when you make such a signal with a uP or whatever.

A big issue is syncing the two video streams.

Graham

I hear that the Propeller from Parallax can create VGA signals, with ok quality.

-Kit

You can certainly generate slow video - i.e., longer line and frame times, which is what I think you're getting at in the above - but the LCD monitor very likely will not accept it. The LCD panel itself has a fairly limited range of timings over which it will operate, and generally the scaler/controller IC typically found in the front end also will accept only a certain range of timings. Most often, the bottom end of that range isn't too far removed from the

60 Hz VGA standard (640 x 480 pixels, 25.175 MHz pixel rate, and about 31.5 kHz horizontal (line) rate).

Bob M.

...

These will depend on how you set the parameters for your sync generator, and you'd have to modify the horizontal and vertical scan oscillators and probably deflection amps to make them scan slower.

This is called "slow-scan TV" - it's a way to put a TV pic on an audio bandwidth. But you need a very long persistence phosphor.

Have Fun! Rich

Phosphor? What's that? :-)

Actually, these days (with memory and other digital bits so cheap), it's a lot more common simply to decode the SSTV and shove it into a frame buffer, then display it on a standard monitor, running at a more normal rate.

Bob M.

Oh, well, that's different!

Never Mind!

Emily Litella ;-)