It can be a challenge to interface 5volt stuff with modern 3.3volt microcontrollers like an ARM or MSP430. This app note covers several circuits for voltage translation on input, output, and bidirectional pins. [via]
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.
Interfacing a 3volt microcontroller to 5volt peripherals - [Link]