arduino_new:
Aren't keypad pins and lcd pins overlapping?
No, it seems. This part is for connecting LCD to Serial I2C LCD Display Adapter only:
#define I2C_ADDR 0x3F // Add your address here. Find it from I2C Scanner
#define BACKLIGHT_PIN 3
#define En_pin 2
#define Rw_pin 1
#define Rs_pin 0
#define D4_pin 4
#define D5_pin 5
#define D6_pin 6
#define D7_pin 7
2 to 9 pins I use for a keypad.
10 pin is set as Interrupt for a coin acceptor.
11-13 - SPI for SD shield.
DAC0, DAC1 - sound.
And I communicate with I2C LCD adapter through 20 & 21 pins.
"The Arduino Due has two I2C / TWI interfaces SDA1 and SCL1 are near to the AREF pin and the additional one is on pins 20 and 21."