USB3450

DS00002105A-page 30

6.12

Detection of Resume

Resume signaling always takes place in FS mode (TERMSELECT and XCVRSELECT = FS enabled), so the behavior

for a HS device is identical to that of a FS device. The Link uses the LINESTATE signals to determine when the USB

transitions from the 'J' to the 'K' state and finally to the terminating FS EOP (SE0 for 1.25us-1.5µs.).

The resume signaling (FS 'K') will be asserted for at least 20ms. At the beginning of this period the Link may negate

SUSPENDN, allowing the transceiver (and its oscillator) to power up and stabilize.

The FS EOP condition is relatively short. Links that simply look for an SE0 condition to exit suspend mode do not nec-

essarily give the transceiver’s clock generator enough time to stabilize. It is recommended that all Link implementations

key off the 'J' to 'K' transition for exiting suspend mode (SUSPENDN = 1). And within 1.25µs after the transition to the

SE0 state (low-speed EOP) the Link must enable normal operation, i.e. enter HS or FS mode depending on the mode

the device was in when it was suspended.

If the device was in FS mode: then the Link leaves the FS terminations enabled. After the SE0 expires, the downstream

port will assert a J state for one low-speed bit time, and the bus will enter a FS Idle state (maintained by the FS termi-

nations).

If the device was in HS mode: then the Link must switch to the FS terminations before the SE0 expires (< 1.25µs). After

the SE0 expires, the bus will then enter a HS IDLE state (maintained by the HS terminations).

6.13

HS Device Attach

Figure 6-8 demonstrates the timing of the USB3450 control signals during a device attach event. When a HS device is

attached to an upstream port, power is asserted to the device and the device sets XCVRSELECT and TERMSELECT

to FS mode (time T1).

ational range as defined in the Hi-Speed specification. The assertion of Device Reset (T0) by the upstream port will ini-

tialize the device. By monitoring LINESTATE, the Link state machine knows to set the XCVRSELECT and

TERMSELECT signals to FS mode (T1).

The standard FS technique of using a pull-up resistor on DP to signal the attach of a FS device is employed. The Link

must then check the LINESTATE signals for SE0. If LINESTATE = SE0 is asserted at time T2 then the upstream port is

forcing the reset state to the device (i.e. Driven SE0). The device will then reset itself before initiating the HS Detection

Handshake protocol.

TABLE 6-9:

RESUME TIMING VALUES (HS MODE)

Timing Parameter

Description

Value

T0

Internal device event initiating the resume process 0 (reference)

T1

Device asserts FS 'K' on the bus to signal resume

request to downstream port

T0 < T1 < T0 + 10ms.

T2

The device releases FS 'K' on the bus. However

by this time the 'K' state is held by downstream

port.

T1 + 1.0ms < T2 < T1 + 15ms

T3

Downstream port asserts SE0.

T1 + 20ms

T4

Latest time at which a device, which was

previously in HS mode, must restore HS mode

after bus activity stops.

T3 + 1.33µs {2 Low-speed bit times}