USB3450

DS00002105A-page 22

The only exception to this is when OPMODE[1:0] is set to state 2 while TXVALID has been asserted (the transceiver is

transmitting a packet), in order to flag a transmission error. In this case, the USB3450 has already transmitted the SYNC

pattern so upon negation of TXVALID the EOP must also be transmitted to properly terminate the packet. Changing the

OPMODE[1:0] signals under all other conditions, while the transceiver is transmitting or receiving data will generate

undefined results.

6.3

Test Mode Support

6.4

SE0 Handling

For FS operation, IDLE is a J state on the bus. SE0 is used as part of the EOP or to indicate reset. When asserted in

an EOP, SE0 is never asserted for more than 2 bit times. The assertion of SE0 for more than 2.5us is interpreted as a

reset by the device operating in FS mode.

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.

6.5

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 Link 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.

TABLE 6-3:

HI-SPEED TEST MODES

Hi-Speed Test Modes

USB3450 Setup

Operational Mode

Link Transmitted Data

XCVRSELECT &

TERMSELECT

SE0_NAK

State 0

No transmit

HS

J

State 2

All '1's

HS

K

State 2

All '0's

HS

Test_Packet

State 0

Test Packet data

HS

FIGURE 6-1:

RESET TIMING BEHAVIOR (HS MODE)