DS00002142A-page 27

USB3250

8.0

APPLICATION NOTES

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

plete description and specifications consult the USB 2.0 Transceiver Macrocell Interface Specification and Universal

Serial Bus Specification Revision 2.0.

8.1

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 USB 2.0 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 USB3250, 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 SIE monitors LINESTATE[1:0] for the IDLE state.

To minimize transitions on LINESTATE[1:0] while in HS mode, the presence of !Squelch is used to force LINES-

TATE[1:0] to a J state.

8.2

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 (state 2), OPMODES are set, and then 5 60MHz clocks later, TXVALID is asserted. In

this case, the SYNC and EOP patterns are not transmitted.

TABLE 8-1:

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

Differential Receiver

Output

1

0

K

Invalid

!Squelch & !HS

Differential Receiver

Output

1

1

SE1

Invalid

Invalid

TABLE 8-2:

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 TXDATA bus become 'J's on the DP/DM

and 0's become 'K's

11

3

Reserved

N/A