DS00002142A-page 29

USB3250

8.5

Reset Detection

bit 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.

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)

T1

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

T2

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

T2

T0

T1