Understanding PPM vs PWM

I’m sure this has been answered but I just can’t find it.
I have Devo F12E…12 channel TX and I have the option of using a normal 12 ch RX or a 7 channel PPM RX. The 7 ch PPM has the PPM outputs plus 7 AUX PWM outputs.
So how many channels is the PPM actually sending to the FC?
I have been trying to research PPM rx’s but I’m not having a lot of luck. So I figure the Pixhawk people here are the experts !

There is a simple way to separate PWM and PPM:

  • PWM = One(1) single channel, can be used directly with servos etc…
  • PPM = Multiple channels put together. Only for autopilots, ppm encoders etc…

How many channels your TX is outputting on PPM signal depends of the TX it self. Some TXes have 8 channels but like you said “7 channel PPM RX” so most likely your TX is outputting channels 1-7 on it’s PPM output.

There’s a nice picture that tell’s it a bit more.

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