Decode a DCC signal. It does not check if a signal is a valid signal. The found packet is transmitted to debug channel and as UDP broadcast packet.

Pin 2 of Port B (INT2) is used to catch interrupts.

A DCC signal 1 typically looks like this:

      _________
0 ___|         |          ___
               |_________|
     '- 56 us -'- 56 us -'

A DCC signal 0 typically looks like this:

     _________________
0 __|                 |                  ___
                      |_________________|
    '---- 100 us -----'---- 100 us -----'

In our schematic we only look at the upper half of the signal. So a DCC signal with 2x 1 looks like this to us:

      _________           _________
0 ___|         |_________|         |_____________
     '- 56 us -'- 56 us -'- 56 us -'- 56 us -'

If we want to know if it is a 1 or a 0 we assume the signal is a 1 (56 us) and check between two 1 blocks:

      _________           _________
0 ___|         |_________|         |_____________
     ^- INT2        ^- check high/low state of pin

If the signal is a DCC 1, the pin should be low. If the signal is a DCC 0, the pin should be high as the length of a DCC 0 (100 us) has not passed yet.