USB3250 datasheet(34/48 Pages) SMSC

34 / 48 page

USB2.0 PHY IC

Datasheet

Revision 1.5 (03-24-06)

SMSC GT3200, SMSC USB3250

DATASHEET

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.

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

Figure 8.1 Reset Timing Behavior (HS Mode)

Table 8.4 Reset Timing Values (HS Mode)

TIMING

PARAMETER

DESCRIPTION

VALUE

HS Reset T0

Bus activity ceases, signaling either a reset or a

SUSPEND.

0 (reference)

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

Driven SE0

HS Detection

Handshake

XCVRSELECT

DP/DM

TERMSELECT

time

Last

Activity

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