High and Low Levels
Transmit
On low and full speed devices
A differential ‘1’ is transmitted by pulling D+ over 2.8V with a 15K ohm resistor pulled to ground and D- under 0.3V with a 1.5K ohm resistor pulled to 3.6V.
A differential ‘0’ on the other hand is a D- greater than 2.8V and a D+ less than 0.3V with the same appropriate pull down/up resistors.
Low-speed and full-speed:
VOD: 0.0V to 0.3 V
VOH: 2.8V to 3.6 V
Receive
The receiver defines a differential ‘1’ as D+ 200mV greater than D- and a differential ‘0’ as D+ 200mV less than D-.
3V3 or 5V?
The transmit logic levels have nothing really to do with either 5V or 3V3 logic systems, but tranceiver compatibility with 5V and 3V3 systems is possible due to the voltage levels used.
USEFUL?
We benefit hugely from resources on the web so we decided we should try and give back some of our knowledge and resources to the community by opening up many of our company’s internal notes and libraries through mini sites like this. We hope you find the site helpful.
Please feel free to comment if you can add help to this page or point out issues and solutions you have found, but please note that we do not provide support on this site. If you need help with a problem please use one of the many online forums.