USB3500

DS00002103A-page 34

To generate resume signaling (FS 'K') the device is placed in the “Disable Bit Stuffing and NRZI encoding” Operational

Mode (OPMODE [1:0] = 10), TERMSELECT and XCVRSELECT must be in FS mode, TXVALID asserted, and all 0's

data is presented on the DATA bus for at least 1ms (T1 - T2).

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).

FIGURE 6-7:

RESUME TIMING BEHAVIOR (HS MODE)

TABLE 6-10:

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}