Something about PIN in Reprapfirmwareconfused

I am confused about the pins defined in Reprapfirmware.FOR EXAMPLE:
#define STEP_PINS {14, 25, 5, X2, 41, 39, X4, 49}
#define DIRECTION_PINS {15, 26, 4, X3, 35, 53, 51, 48}
I can not figure out the relationship between the duet and the pin numbers.Are these pin numbers defined in the Reprapfirmware?
I want to change the pin numbers about Z PROBE,I must figure out the pin numbers according to the duet.
PLEASE give me some advices.
Sorry for my poor English.

The firmware uses the Arduino Due core to write to most of the pins. For the standard pins (those with plain numbers, not prefixed by 'X'), the mapping is defined at [arduino.cc]. For the pin numbers beginning with X, it is defined in file Libraries/SamNonDuePin/SamNonDuePin.cpp.

I am very tempted to stop using the Arduino core in my fork of the firmware and call the underlying Atmel Software Framework functions instead; because I've already had to patch or bypass the Arduino core in several places, either to fix bugs or to add missing functionality Then I would number the PORTA pins 0-31, the PORTB pins 32-63 and so on. This is what I have done in the firmware for the TFT controller board.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Dear DC42,you are so helpful.Thank you for your advice!!!