USB3250

DS00002142A-page 30

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 SIE must then check LINESTATE for

the J condition. If J is asserted at time T2, then the upstream port is asserting a soft SE0 and the USB is in a J state

indicating a suspend condition. By time T4 the device must be fully suspended.

8.7

HS Detection Handshake

The High Speed Detection Handshake process is entered from one of three states: suspend, active FS or active HS.

The downstream facing port asserting an SE0 state on the bus initiates the HS Detection Handshake. Depending on

the initial state, an SE0 condition can be asserted from 0 to 4 ms before initiating the HS Detection Handshake. These

states are described in the USB 2.0 specification.

There are three ways in which a device may enter the HS Handshake Detection process:

1.

If the device is suspended and it detects an SE0 state on the bus it may immediately enter the HS handshake

detection process.

2.

If the device is in FS mode and an SE0 state is detected for more than 2.5µs. it may enter the HS handshake

detection process.

FIGURE 8-2:

SUSPEND TIMING BEHAVIOR (HS MODE)

TABLE 8-5:

SUSPEND TIMING VALUES (HS MODE)

Timing Parameter

Description

Value

HS Reset T0

End of last bus activity, signaling either a reset or a

SUSPEND.

0 (reference)

T1

The time at which the device must 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 = 'J', then the

initial SE0 on the bus (T0 - T1) had been due to a

Suspend state and the SIE remains in HS mode.

T1 + 100 µs < T2 < T1 + 875µs

T3

The earliest time where a device can issue Resume

signaling.

HS Reset T0 + 5ms

T4

The latest time that a device must actually be

suspended, drawing no more than the suspend current

from the bus.

HS Reset T0 + 10ms

Last

Activity

'J' State

Soft SE0

Device is suspended

SUSPENDN

XCVRSELECT

DP/DM

TERMSELECT

time

T2

T0

T1

T3

T4