I've attached a GIF showing the output waveform from the HT640 sending all ONES, all ZEROS, all ELSE, and repeating those three in ONE, ZERO, ELSE order.
First, you have to pick the start sequence out of the air (usually signals are sent 3-5 times with the first few setting the receiver AGC) and then capture and decipher the following bitstream. You might do this using the CCP hardware in Capture mode, resetting the polarity after each interrupt but it's not a simple task.
As you can see there are two different pulse widths and two different space widths. The actual widths will depend on the transmitter oscillator frequency.
The best advice is to use the Holtek decoder chip with the same oscillator frequency as used by the transmitter.
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