When interfacing between two devices such as a Raspberry Pi with 3V3 I/O and a PICMicro running at 5V voltage level conversion is necessary. A simple method to do this on a breadboard is to use a pre-built adapter.

Two of the more popular types found at places like eBay are two channel bi-directional I2C level converters and four channel general purpose converters.

These devices contain two mosfets with pull-ups resistors in the arrangement specified by the Philips I2C interfacing application note (link below).

They also have an additional component which is a 3V3 LDO voltage regulator. This addition is to allow a 5V device to directly interface with a 3V3 device and also power it.

The LDO has only been tested to drive an LED and it's not known whether the LDOs present are genuine and can be relied upon.

Although marketed for I2C they can be used for anything that demands two channels of bi-directional voltage level conversion.

3V3 OUTPUT  BVCC    AVCC  5V INPUT
3V3 CLOCK   BSCL    ASCL  5V CLOCK
3V3 DATA    BSDA    ASDA  5V DATA
GROUND      BGND    AGND  GROUND

There is a speed impact when using these device which have a slow rise time. For example, when using Pickle Microchip PIC ICSP it was found that raising the SLEEP configuration value to 8 was necessary.

Level shifting techniques in I2C-bus design