USB3500

DS00002103A-page 36

6.14

USB Reset and Chirp

The USB 2.0 specification describes USB Reset as a means of attaching a FS or a HS Device to a Host. This discussion

will focus on a HS device connecting to a HS host.

Figure 6-9 shows the UTMI+ interface for both a Host (DPPD & DMPD = 1) and a Device (DPPD & DMPD = 0). The

following discussion applies to when the USB3500 is a configured as a Device and is connected to another USB3500

configured as a Host. Since the Host and Device negotiate this transition, both are discussed together and the user may

follow this discussion for either a host or device depending on the application of the USB3500. This sequence is also

referred to as a “high-speed chirp” due to the K-J pairs which the host sends to the downstream device.

Before the Host begins a session, it will set Xcvrselect to FS mode (10b) and Termselect to 1b to activate the HS termi-

nation. The Host will also asserted the 15Kohm pull-down resistors on DP and DM. The 15Kohm pull down resistors will

pull DP and DM to 0 volts so that the Host Linestate will return Single Ended Zero (SE0) when nothing is attached.

At time marker T0, the host link applies VBUS to the downstream port.

At T1, the Device has detected a valid voltage on VBUS and has asserted Termselect to enable the 1.5K ohm pull-up

resistor on DP. During T1 the Host sees the linestate go from SEO to a J due to the pull-up on DP.

FIGURE 6-9:

USB RESET AND CHIRP

Note:

Note: Should a device attached to the host be a LS device, then the 1.5 K ohm pull-up is applied to DM.

The following discussion does not apply to a LS device attached.

xcvrselect

termselect

opmode

txvalid

data

vbus

xcvrselect

termselect

opmode

txvalid

linestate

data

T1

T0

T2

5Volt

SE0

01

00

01

00

10

J

SE0

T3

T4

00h

Kseo

T5

KJ

K

J

T6

T7

T8

K

00

FF

FF

00

00

rxactive

rxvalid

00

10

00

DP

DM

K-J

Pairs

J

00

SE0

00-FF

HS

SOF

A5h

00

Hs SOF packet

Hs SOF packet

00h