When you go to EE school, you actually spend at least one whole semester studying signals.
For this exercise we need to nail down 2 concepts. The first is the concept of periodic waveform, it's period, waveform, etc. And the average or RMS value over that period.
RC Servos and Motors, and our FRC/VEX equipment all use the RC PWM scheme of control. It doesn't work on RMS values. Remember the period can be 20 ms but only about 2ms of that signal has our useful control information.
Standard PWM is essentially RMS value. If you have had calculus you will cover a concept called integration that calculates the area under the curve. You could actually perform an RC lowpass function on it and create a dc voltage that corresponds to the duty cycle. The RC lowpass is actually implements an integral and performs this RMS average.
You can see a sample of the circuit and the waveforms here :
http://controls.ame.nd.edu/microcont...in/node41.html
Modern logic and analog chips are usually implemented with CMOS gates (sometime JFET gates, rarely bipolar junctions) and have a very high input impedance which is what you are talking about here. The spec sheet is telling you the maximum current the pin will draw. What that means here is that you don't need a diesel engine to drive this gate. It can greatly simplify the nature of the signal source needed to drive this input.
You are not going to have any trouble driving this pin. You do need a way to translate the RC PWM to standard PWM.
I suspect this goofy RC PWM waveform had something to do with hobby RC systems decades ago and how they multiplexed multiple control channels onto a single RF carrier for broadcast.
You probably have 2 ways to solve the problem. The first would be some sort of creative analog circuit. The second would be to take a small processor with a fast interrupt to sample the pin and synthetically create a standard PWM output. Either of these is a very educational project if you have never done it before.
Here is a useful bit if information: I think I referenced the paul.hills website before, but here is a specific reference translating the RC PWM.
http://homepages.which.net/~paul.hil...RxDecoder.html
I'm back and editing this post I did previously.
Above the Paul Hills link shows several ways to decode an RC PWM signal. One method gives you an analog output, the other a digital word.
Ok, so lets say you do the analog output thing. Now you need to create the standard PWM. So you need a voltage controlled PWM generator.
Back to Paul Hills at this link:
http://homepages.which.net/~paul.hil...enerators.html
Between these two pages, you have a RC PWM to voltage decoder and a voltage to standard PWM encoder.
If you nail these two pages then you will be 'the man'. There is quite a bit of material there. If you could get an inexpensive scope and a breadboard and a pile of parts you would be on the way.
Ed