In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Tracy Allen wrote:

The input will need to be pretty clean.   I'd suggest you add another comparator or schmitt trigger before the MAX3100 input, in order to square up the signal and to be sure the pulses are sufficient height and also width.

Another thing about the MAX3100 IRDA is that it requires the input pulses to be at least 3/16 of the bit duration.   So at 9600  baud, each pulse should be at least 20 microseconds long, or it will not register.   The relaxed version of the IRDA standard allows pulses as short as 1.6 microseconds at any baud rate, for power conservation.    The Palm in general accepts the shorter pulses, and the keyboard might send shorter pulses.  

Your receive circuit evidently is doing some RC pulse stretching, which may be a good thing.   You just need a comparator to make the pulses long enough and solidly down to 0 volts.

I don't know what to think about the protocol.   Have you dug into Google to find info about it?   I have Palm developer docs, but they doesn't seem to  "touch" on the keyboard.

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