USB3280

DS00001898A-page 30

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8.9

HS Detection Handshake – HS Downstream Facing Port

Upon entering the HS Detection process (T0) XCVRSELECT and TERMSELECT are in FS mode. The DP pull-up is

asserted and the HS terminations are disabled. The SIE then sets OPMODE to Disable Bit Stuffing and NRZI encoding,

XCVRSELECT to HS mode, and begins the transmission of all 0's data, which asserts a HS K (chirp) on the bus (T1).

The device chirp must last at least 1.0ms, and must end no later than 7.0ms after HS Reset T0. At time T1 the device

begins listening for a chirp sequence from the downstream facing port. If the downstream facing port is HS capable then

it will begin generating an alternating sequence of Chirp K’s and Chirp J’s (T3) after the termination of the chirp from the

device (T2). After the device sees the valid chirp sequence Chirp K-J-K-J-K-J (T6), it will enter HS mode by setting

TERMSELECT to HS mode (T7).

Figure 8-4 provides a state diagram for Chirp K-J-K-J-K-J validation. Prior to the end of reset (T9) the device port must

terminate the sequence of Chirp K’s and Chirp J’s (T8) and assert SE0 (T8-T9). Note that the sequence of Chirp K’s

and Chirp J’s constitutes bus activity.

The Chirp K-J-K-J-K-J sequence occurs too slow to propagate through the serial data path, therefore LINESTATE signal

transitions must be used by the SIE to step through the Chirp K-J-K-J-K-J state diagram, where "K State" is equivalent

to LINESTATE = K State and "J State" is equivalent to LINESTATE = J State. The SIE must employ a counter (Chirp

Count) to count the number of Chirp K and Chirp J states. Note that LINESTATE does not filter the bus signals so the

requirement that a bus state must be "continuously asserted for 2.5µs" must be verified by the SIE sampling the LIN-

ESTATE signals.

FIGURE 8-4:

CHIRP K-J-K-J-K-J SEQUENCE DETECTION STATE DIAGRAM

Detect K?

Start Chirp

K-J-K-J-K-J

detection

INC Chirp

Count

K State

!K

Detect J?

INC Chirp

Count

J State

!J

Chirp Count != 6

& !SE0

Chirp Count

= 0

Chirp Count != 6

& !SE0

Chirp Valid

Chirp

Invalid

SE0

Chirp Count