DS00002103A-page 37

USB3500

At T2, the Host has detected the FS device attached to the USB bus. At this time the Host will reset the bus by driving

a SE0. The SE0 is created by switching to HS Mode and activating the HS termination by de-asserting Termselect. The

45 ohm high speed terminations pull the bus to SE0.

At T3, the Device will respond to the SE0 by driving a “Device Chirp K” onto the bus. The “Device Chirp K” is driven with

Opmode = 10b so that bitstuffing and NRZI encoding is disabled.

During T3 the HS host will see the “Device Chirp K” and prepare to respond to the device by setting Opmode = 10b to

disable the bitstuffing and NRZI encoding.

At T4, the Device will stop driving a the Chirp K, letting the bus return to SE0, and wait for the Host to respond. The

device removes the K by de-asserting Txvalid. The device will have driven the K for a minimum of 1mS. The Host sees

the linestate change from K to SE0.

At T5, the host begins transmitting K-J pairs to the device. Each K or J is 40-60uS long and the K-J pairs are repeated

for the remainder of the 10mS USB reset.

At T6, the device has detected 3 K-J pairs. The device switches the Termselect low and changes Opmode to 00b. The

device is now in high speed and waits for the first SOF packet from the upstream host. When Termselect is de-asserted,

the HS termination is activated which lowers the amplitude of the K-J pairs.

At T7, the host ends the K-J pairs and switches to normal HS mode by changing Opmode to 00b.

At T8, the Host sends the first SOF packet. This is done by putting the SOF PID 0xA5 on the data bus and asserting

Txvalid. The link transfers the SOF packet. After, the SOF packet a normal high speed USB session started.