#define X_STEP_PIN         54
#define X_DIR_PIN          55
#define X_ENABLE_PIN       38
#define X_MIN_PIN           3
#define X_MAX_PIN           2

Name      software pin  Mega2560 board label
X_STEP_PIN    54         Analog A0
X_DIR_PIN     55         Analog A1
X_ENABLE_PIN  38         Digital 38
X_MIN_PIN     3          PWM 3
X_MAX_PIN     2          PWM 2