Serial Communication between 5v and 3.3v logic

Im working on a project that is using a Rabit microcontroller that runs on 3.3v logic and im wondering if there is anything special I need to do to be able to connect an Arduino Duemilanove to it using serial communication.

The Rabit is the master microcontroller and it will periodically ask the arduino for information. Im not too familiar with serial communication but im thinking i will need a 3.3v to 5v logic level converter for this to work correctly?

Is my assumption correct or will i just be able to connect the TX directly to the Rx?

Thanks in advance


Hi Chris;

You can wire the Rabbit's serial output directly to the Arduino's serial input pin as the Arduino will consider a 3.3 volt high as a valid high state. Wiring the Arduino's serial output (5vdc) to the Rabbit takes a little research. Some 3.3 v devices are 5volt 'tolerant' on their input pins but you need to research their data sheet to see if this is the case. If it is not 5volt tolerant then a simple method is to wire the Arduino's serial output to two series connected resistors wired to ground. The resistors can be sized such that the junction of the two resistors forms a voltage divider that will be 3.3vdc when the divider is driven to 5vdc and this can be wired directly to the Rabbits serial input pin.

Make sense?


Yeah that makes sense. I guess its even easier than I thought. Thanks for the help.