Using the W5100 at 3V3 P.S.. needs SPI voltage buffers/level converter?

Other Hardware Hardware Development
2

The W5100 runs on 3.0V to 3.6V so you don't need any conversion to connect it to a 3.3V processor. The inputs are also "5V Tolerant" so you don't need any conversion to connect it to a 5V processor.