Electronic – Is fractional PLL the key functionality that defines whether a microcontroller is able to generate an analog TV signal

microcontrollerntscpllprogrammable-logic

I've been researching microcontrollers with the goal of outputting NTSC and/or PAL video signals.

And when I look at the microcontroller specifications, it appears to me that the single most important factor in determining if a microcontroller can generate analog video, is whether or not it has a clock/PLL/timer/counter that can be divided/multiplied such that somehow it is able to output a frequency that matches the required NTSC/PAL video frequency.

And more specifically, it needs the PLL to be fractional so that the clock timers can be divided very precisely because video requires very precise timing.

Is this correct? Am I on the right track, that basically, a microcontroller with a fractional PLL is able to generate NTSC/PAL video, whilst a microcontroller without fractional PLL is not able to generate NTSC/PAL video?

Or do I have it wrong, is the fractional PLL not so important, maybe the required frequency can be generated in some other way that would match the analog frequencies?

Clarification 1:

I am trying to identify, when I look at the specs of a microcontroller, if it is, or is not able to generate an analog video signal. I do understand that many other factors are important in working out if it can do so, but my understanding is, that if you cannot control the output frequency of one of the peripherals to an analog TV output frequency, then nothing else matters – the job cannot be done. I am trying to confirm if my understanding is correct or not.

Clarification 2:

What I am really trying to understand is whether any given MCU can generate the required frequencies without using external components – such as providing an external clock crystal.

Clarification 3:

I'm talking abut generating a composite signal.

Best Answer

Of course not. You always have the option of running the MCU's main clock at the required frequency (or a multiple thereof) so that everything else can be derived by simple counters.

The MCU datasheet will show you the external clock input along with the range of frequencies that you may apply to it. Pick a frequency within that range for your external crystal or oscillator that meets the needs of your application.

For example, a frequency of 14.31818 MHz (4 × the 3.579545 MHz color subcarrier) might be a good choice for generating NTSC video.

MCUs that do serial communication over UARTs frequently run at frequencies like 11.0592 MHz, which is a multiple (6×) of 16 × 115200 Hz that happens to be less than 12 MHz, the upper limit of a common MCU back in the day. If your MCU can do 20 MHz, you might choose 18.432 MHz (10×) instead.