• Composite Video from AVR?
    3 replies, posted
I'd like to start by saying I'm not a specialist at doing anything with microcontrollers, so tell me if I'm wrong. I'm planning to make a "video card", actually just an AVR microcontroller making a Composite video signalling so funny things can be drawn on a screen So here is what I think so far: Composite video means 780 x 460 pixels at 60 herts. That means an analog signal has to change at a rate of over 20 MHz. This also means 350 000ish pixels. So, my idea is using two 256 KB ram chips connected to some form of counter-timer working at 20 MHz repeatedly feeding the image data into a crude digital to analog converter, and then mixed with syncing signal and into the cable. Hopefully the syncing can also be done with counters without involving the ATTiny (I don't have many of those...) Now the ATTiny2313V there is going to accept commands from one port at a much slower rate and with a clock wire for commands which makes it much less painful to work with. According to these commands the ATtiny is going to draw lines, rectangles, text and other fancy stuff procedurally at it's own pace. This way, the memory chips act as a "slow down gate" and the ATtiny is then a GPU. Good plan? If no, why?
You're probably going to need extra hardware. The ATTiny can't output a 20MHz signal on its own (unless it's something totally trivial). At the very least, you'll need a PISO shift register. Also, isn't composite video RF? So you're probably going to need a modulator too. Also, you should've posted this in the programming subforum. It moves slower so it won't get shoved off the page in an hour, and the people who post there are generally more knowledgeable at this sort of thing.
I know, and that's why I thought of generating the signal off a memory chip while having the ATTiny write to it (or a different chip and then switch them like buffers?) at speeds much slower than 20 MHz. By the way, is there a way to change PAL resolution? So that I could do say a 256x198 picture instead? That would give me plenty of time. Edit: after reading more on PAL generation I found out I can quite easily make a 640x256 image while allowing memory chips 70ns to prepare new data. More on it in a weeks time.
Does it have to be composite video? I think VGA might be a lot easier to work with, and it's been done before on an AVR. I found a sorta high-level/overview article on an AVR outputting both VGA and RCA video: [url]http://www.atmel.com/journal/documents/issue6/Pg40_42_VideoAdapter.pdf[/url]
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