Freescale Semiconductor TWR-MCF52259-Ethenet User Manual page 113

• USB uses Non-Return to Zero, Inverted signaling
– Separate clock signal not required to be delivered with data
– '1' on the data line indicates no change in level of NRZI signal
– '0' on the data line indicates transition in level of NRZI signal
– Long string of 1s will eventually cause receiver to lose
synchronization
Idle 0
Data
NRZI
1 1 0 1 0
TM
0 0 1 1 1 0