basic connection question - basic work voltage of arduino due

hello everyone, i am working on a little project where i use a pololu maestro 12 channels servocontroller to contol several servos and a EASYDRIVER STEPPER MOTOR DRIVER to control a stepper motor. Both platform works at a 5V basic voltage, and i know that it might be a problem to connect them to an input pin of my arduino due. The question is, what is the risk of connecting them only to output pins of the arduino and controll them with 3.3V based ttl. (it might not work/ damage the arduino). thanks a lot!

You will damage/destroy the Due if you put 5V on any of its pins - the chip cannot tolerate this voltage at all.

even if i use only one direction communication - from the arduino to the devices (only tx pin connected in the arduino)? thank you

That would work, but you have to be absolutely sure you never back drive that wire. I would add a 2k2 resistor in series with the connection to prevent damage should that happen - Due's are expensive.

The process used for the Due chip is not 5V tolerant - the core is 1.8V and the IO drivers are 3.3V with absolute max of 4.0V. In practice that means 3.3V maximum.

Thank you very much for fast answer!