I2C interfacing with ATmega32 and ArduinoMega2560 failed
In PIC code as slave I2C, use:

i2c(Slave, sda=PIN_C4, scl=PIN_C3, address=0xa0, FORCE_HW, FAST);


In Arduino code as master I2C, use:

const int SLAVE_ADDRESS2 = 0xA0;  // esclavo PIC
Wire.beginTransmission(SLAVE_ADDRESS2 &gt;&gt; 1);