USB2.0 PHY IC
For HS operation, IDLE is a SE0 state on the bus. SE0 is also used to reset a HS device. A HS
device cannot use the 2.5us assertion of SE0 (as defined for FS operation) to indicate reset since the
bus is often in this state between packets. If no bus activity (IDLE) is detected for more than 3ms, a
HS device must determine whether the downstream facing port is signaling a suspend or a reset. The
following section details how this determination is made. If a reset is signaled, the HS device will then
initiate the HS Detection Handshake protocol.
8.5
Reset Detection
If a device in HS mode detects bus inactivity for more than 3ms (T1), it reverts to FS mode. This
enables the FS pull-up on the DP line in an attempt to assert a continuous FS J state on the bus. The
SIE must then check LINESTATE for the SE0 condition. If SE0 is asserted at time T2, then the
upstream port is forcing the reset state to the device (i.e., a Driven SE0). The device will then initiate
the HS detection handshake protocol.
T0
T2
T1
time
XCVRSELECT
TERMSELECT
DP/DM
Last
Activity
Driven SE0
HS Detection
Handshake
Figure 8.1 Reset Timing Behavior (HS Mode)
Table 8.4 Reset Timing Values (HS Mode)
DESCRIPTION
TIMING
PARAMETER
VALUE
HS Reset T0
Bus activity ceases, signaling either a reset or a
SUSPEND.
0 (reference)
T1
T2
Earliest time at which the device may place itself in
FS mode after bus activity stops.
HS Reset T0 + 3. 0ms < T1 < HS
Reset T0 + 3.125ms
SIE samples LINESTATE. If LINESTATE = SE0, then
the SE0 on the bus is due to a Reset state. The
device now enters the HS Detection Handshake
protocol.
T1 + 100µs < T2 < T1 + 875µs
8.6
Suspend Detection
If a HS device detects SE0 asserted on the bus for more than 3ms (T1), it reverts to FS mode. This
enables the FS pull-up on the DP line in an attempt to assert a continuous FS J state on the bus. The
Revision 1.3 (10-05-04)
SMSC GT3200, SMSC USB3250
DATA2S9HEET
SMSC [ SMSC CORPORATION ]
