Hi
thanks for the reply.
The code I sent you above is working pretty well on arduino Mega using HARDWARE SERIAL.
The MCU on the back of the Nextion is a 3.3V chip (STM32F030C8T6 powered after the 3.3V regulator) so this is why I dont understand why it does not work.
The only difference between the MEGA and the DUE I can see on the serial pins is that on the MEGA all serial pins are 5V TTL and on the DUE pins 0 and 1 are 5V and the other 3 are 3V TTL.