Texas Instrument nous propose une note d’application qui explique comment interfacer  un circuit 5V avec des périphériques 3V3.

The interfacing of the 3-V MSP430x1xx and MSP430x4xx  microcontroller families to circuits with a supply of 5 V or  higher is shown. Input, output and I/O interfaces are given and explained. Worst-case design equations are provided, where  necessary. Some simple power supplies generating both voltages are shown, too.