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One way is to use a 8 bit counter when the counter starts, a flip-flop must be set to high. The counter start counting. When the counter reach the value of your 8 bit digital then reset the flip-flop. When the counter finish counting, then reset the counter and set the flip flop again.
Well I don't know if there are any integrated cicuits that perform this kind of operation besides a microcontroller like a PIC, in which you can take a digital input through any of it's ports and then use it's internal PWM to generate the signal. Using a microcontroller just to do this would be a waste of hardware (money) but it's the easiest way. If you want to start from scratch you could use a DAC to convert your 8-bits onto a DC voltaje (equivalent to the 8-bit number), then take a sawtooth wave (if you can't find an integrated circuit for this you could use the application notes from the OTA LM13700 and build it yourself), then take that signal and use a comparator to generate a pulse wave (with the pulse with proportional to the 8-bit number you had).
I'm not sure, but I don't think so, cause with the V/F converter you're varing a frequency with an input voltaje but not the pulse with. What you want is constant frequency, diferent duty cycle.
Use a resistor ladder to convert to analog voltage. Then compare the analog voltage to a triangle or ramp signal from an oscillator circuit. The output of the comparator will be PWM. If you design it right, you will get desired range.
if you can't find an integrated circuit for this you could use the application notes from the OTA LM13700 and build it yourself. There are other several multivibrator configurations in which you can generate that signal.
the frequency of the sawtooth wave should be the same as the one you want on your output signal.
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