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A Video on Video

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Pilot3514:
I don't know if there is a blog in here anywhere but maybe some musings I had a while back may give you some ideas.

I was working on a little project containing a micro controller, I believe it was an Atmel AVR though it might have been a TI MCP430.  The exact controller is unimportant.  There came a point where I thought it would be nice to display some data.  I could of course send it to my computer via an async serial link.  But I thought I would like to display it straight to a monitor or to my TV via a composite video signal.

So I started looking for options.  I thought that what I would really like is a little chip, 8-10 pins, a couple lines for power, a couple lines for I2C interface, maybe a couple pins for a crystal, but not much else.  I couldn't find anything.

I tried to think back to what I had seen in the past.  I remember reading a book written by on of the pioneers of the personal computer revolution, Don Lancaster.  His book "The TV Typewriter" showed how to build a terminal for you computer with discrete TTL logic chips and an old TV. 

I also remembered a computer that I had a long time ago designed by Sir Clive Sinclair.  His ZX80/ZX81 used the main process, a Z80, to generate the video signal.  You programmed it in BASIC and the program would run during the horizontal and vertical blanking times.  If you wanted your program to run faster, there was a command to turn off the screen.

More recently, there has been an Arduino sketch/program called TVOut that uses an ATMega328 to generate very low resolution video text and graphics.  I tried to look at the code behind TVOut but it is a lot of interrupt driven assembler.  With it having so much interrupt driven code, I can not tell if it would impact the serial communication's (UART, I2C, SPI) interrupts or vice versa.

I had hoped that a manufacturer would have adapted one of their micro controllers to make a video output controller.  Many micros have 2K or more of RAM.  That is more than enough for a 24X80 screen.  Even a 16x64 is not bad and that is only 1K.  Obviously if you add color, or graphics then the memory requirements explode.  Maybe in a world of SVGA, HDMI, 1080p and HD there is no interest in old fashion text.

What do you think?  Is there a blog in my ramblings?  Do you have an interest in video signals? 

jucole:
I've been playing around with video signals;  I've been generating very simple PAL bar patterns with a 16f877a and then with a 18f4550;  I'm in the process of designing a basic video driver using a Cyclone II for a new project I'm working on - I need to test the hsync this weekend actually;  I only started with fpga's last week but I'm really starting to like them!

Pilot3514:

--- Quote from: jucole on March 27, 2013, 11:01:11 am ---I've been generating very simple PAL bar patterns ...

--- End quote ---
Are you talking about color test patterns?  I also assume that you are using a composite signal.  I don't know much about video signaling but terms like PAL and hsync sounds like they would only apply to composite.  Well I guess that other forms of video signaling would need to sync the horizontal and vertical.  Even in the Outer Limits.

I assume that the 16f877a are 18f4550 are FPGA's.  Aren't those the big chips with hundreds of I/O leads?  It sounds like those would be hard to work with on the kitchen table.

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