DS00002105A-page 21

USB3450

6.0

APPLICATION NOTES

The following sections consist of select functional explanations to aid in implementing the USB3450 into a system. For

complete description and specifications consult the Hi-Speed Transceiver Macrocell Interface Specification and Univer-

sal Serial Bus Specification Revision 2.0.

6.1

Linestate

The voltage thresholds that the LINESTATE[1:0] signals use to reflect the state of DP and DM depend on the state of

XCVRSELECT. LINESTATE[1:0] uses HS thresholds when the HS transceiver is enabled (XCVRSELECT = 0) and FS

thresholds when the FS transceiver is enabled (XCVRSELECT = 1). There is not a concept of variable single-ended

thresholds in the Hi-Speed specification for HS mode.

The HS receiver is used to detect Chirp J or K, where the output of the HS receiver is always qualified with the Squelch

signal. If squelched, the output of the HS receiver is ignored. In the USB3450, as an alternative to using variable thresh-

olds for the single-ended receivers, the following approach is used.

In HS mode, 3ms of no USB activity (IDLE state) signals a reset. The Link monitors LINESTATE[1:0] for the IDLE state.

to a J state.

6.2

OPMODES

The OPMODE[1:0] pins allow control of the operating modes.

The OPMODE[1:0] signals are normally changed only when the transmitter and the receiver are quiescent, i.e. when

entering a test mode or for a device initiated resume.

When using OPMODE[1:0] = 10 the SYNC and EOP patterns are not transmitted.

TABLE 6-1:

LINESTATE STATES

State of DP/DM Lines

Linestate[1:0]

Full Speed

XCVRSELECT =1

TERMSELECT=1

High Speed

XCVRSELECT =0

TERMSELECT=0

Chirp Mode

XCVRSELECT =0

TERMSELECT=1

LS[1]

LS[0]

0

0

SE0

Squelch

Squelch

0

1

J

Squelch

Squelch &

HS Diff. Receiver Output

1

0

K

Invalid

Squelch &

HS Diff. Receiver Output

1

1

SE1

Invalid

Invalid

TABLE 6-2:

OPERATIONAL MODES

Mode[1:0]

State#

State Name

Description

00

0

Normal Operation

Transceiver operates with normal USB data encoding and

decoding

01

1

Non-Driving

Allows the transceiver logic to support a soft disconnect feature

which tri-states both the HS and FS transmitters, and removes

any termination from the USB making it appear to an upstream

port that the device has been disconnected from the bus

10

2

Disable Bit Stuffing

and NRZI encoding

Disables bitstuffing and NRZI encoding logic so that 1's loaded

from the DATA bus become 'J's on the DP/DM and 0's become

'K's

11

3

Reserved

N/A