jball:
It might change later currently it is 50/sec and that is steady
50/sec is 20ms but is that 50ms HIGH then 50ms LOW over and over or is it a very short blip of LOW every 50ms?
Using direct port read you can monitor the line more than 50 times a millisecond to watch for 20ms pulses going by like turtles. Mitsubishi has a white paper with led to led communications where data 0 is 2 to 4 HIGH reads and data 1 is 7 to 10 HIGH reads, short vs long pulse. Doing that they were able to achieve "rock solid" led to led 250 cps bidirectional comes at range of 5cm or less. PDA's and remotes could talk up close for the cost of a led and a resistor and some code.
You see they sensed he real world redundantly to be sure of their results. And you have the speed to do the same.