PPM TO PWM CONVERSION LOGIC & Vice Versa

Please help how to convert ppm into pwm & vice versa?
Logic would b sufficient;
circuit diagram would be great

thanks
but could not understand anything from the circuit
plz logic behind the circuitry?

PWM first :
If we apply variable voltage at control input (pin 5) of IC555 in astable mode then the width of output pulse will change accordingly. When we apply low frequency audio signal to the control input, internally the control voltage will change the reference voltage of comparator so charging time of capacitor changes every time and so width of o/p pulse also changes. So here as shown in figure the audio signal is applied at the control input through positive clamper circuit. The values of R1, R2 and C1 are chosen to generate pulse train of around 64 KHz.

PPM from PWM:

PPM is simply PWM + monostable multi-vibrator. Means if we fed the PWM output to trigger input of IC555 in monostable mode then the output of monostable will be PPM wave. So to generate PPM we require one astable multi-vibrator to generate PWM signal and one monostable multi-vibrator to get desire PPM.

there are many other ways to do it i just explained the attached circuit.