Explain terms upstream
connection and downstream connection, what is their significance
Explain two types of USB
connectors
Type A
Type B
Explain USB on-the-go feature
Adds peer-to-peer functionality
to USB
Explain electrical attributes
of USB connection
Differential transmission part
for data
Encoded using NRZI and is bit
stuffed to ensure adequate transitions in the data stream
How a differential ‘1’ and ‘0’
are transmitted in Low and full speed devices
‘1’ by pulling D+ over 2.8V
with a 15K ohm resistor pulled to ground; D- under 0.3V with a 1.5K ohm
resistor pulled to 3.6V
‘0’ by pulling D- over 2.8V
with a 1.5K ohm resistor pulled to ground; D+ under 0.3V with a 1.5K ohm
resistor pulled to 3.6V
Explain significance of J, K;
how to identify J & K in LS, HS?
LS: ‘J’ state is a differential
0
HS: ‘J’ state is a differential
1
USB transceivers will have both
differential and single ended outputs
SE0, SE1?
How speed identification works
in USB?
How pull up resistors at D+, D-
used to identify LS, FS devices?
How HS speed negotiation works?
HS devices will start by
connecting as a full speed device (1.5k to 3.3v). Once it has been attached, it
will do a high speed chirp during reset and establish a high speed connection
if the hub supports it. If the device operates in high speed mode, then the
pull up resistor is removed to balance the line.
HS device must not support LS
mode.
How does USB device enter in to
suspend mode?
A USB device will enter suspend
when there is no activity on the bus for greater than 3.0ms. It then has a
further 7ms to shutdown the device and draw no more than the designated suspend
current and thus must be only drawing the rated suspend current from the bus
10mS after bus activity stopped. In order to maintain connected to a suspended
hub or host, the device must still provide power to its pull up speed selection
resistors during suspend.