Fri Feb 4 13:16:18 EST 2011

Interfacing 3V3 and 5V applications.

From [2]: "There are many ICs available on the market that are
specifically designed to translate between logic levels. We've never
used any of them!"

The basic ideas are:

  * 5V -> 3V: use a current limiting resistor.  This requires the 3V3
    input to be protected with clamping diode the 3V power supply!

  * 3V -> 5V: no resistor necessary, inputs are compatible.  I guess
    it doesn't hurt to place one anyway in case master/slave roles are

SPI bus with the 5V device as master, as seen in the example in [2]:

  * MISO: master input slave output (3V)
  * MOSI: master output slave input (5V)
  * SCK:  master clock (5V)

[1] http://www.nxp.com/documents/application_note/AN240.pdf
[2] http://www.sparkfun.com/tutorials/65