USB3370 datasheet(43/75 Pages) MICROCHIP

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DS00001915B-page 43

USB3370

6.4.1.4

Host Resume K

Resume K generation is supported by the USB3370. At the end of a USB Suspend the PHY will drive a K back to the

downstream device. When the USB3370 exits from Low Power Mode, when operating as a host, it will automatically

transmit a Resume K on DP/DM. The transmitters will end the K with SE0 for two Low Speed bit times. If the USB3370

was operating in Hi-Speed mode before the suspend, the host must change to Hi-Speed mode before the SE0 ends.

SE0 is two Low Speed bit times which is about 1.2 us. For more details please see sections 7.1.77 and 7.9 of the USB

Specification.

In device mode, the resume K will not append an SE0, but release the bus to the correct idle state, depending upon the

operational mode as shown in Table 5-1.

The ULPI specification includes a detailed discussion of the resume sequence and the order of operations required. To

support Host start-up of less than 1mS the USB3370 implements the ULPI AutoResume bit in the Interface Control reg-

ister. The default AutoResume state is 0 and this bit should be enabled for Host applications.

6.4.1.5

No SYNC and EOP Generation (OpMode = 11)

UTMI+ defines OpMode = 11 where no sync and EOP generation occurs in Hi-Speed operation. This is an option to the

ULPI specification and not implemented in the USB3370.

6.4.2

TYPICAL USB TRANSMIT WITH ULPI

Figure 6-9 shows a typical USB transmit sequence. A transmit sequence starts by the Link sending a TX CMD where

DATA[7:6]

= 01b, DATA[5:4] = 00b, and Data[3:0] = PID. The TX CMD with the PID is followed by transmit data.

During transmit the PHY will use NXT to control the rate of data flow into the PHY. If the USB3370 pipeline is full or bit-

stuffing causes the data pipeline to overfill NXT is de-asserted and the Link will hold the value on Data until NXT is

asserted. The USB Transmit ends when the Link asserts STP while NXT is asserted.

After the USB3370 completes transmitting, the DP and DM lines return to idle and a RXCMD is returned to the Link so

the inter-packet timers may be updated by linestate.

While operating in Full Speed or Low Speed, an End-of-Packet (EOP) is defined as SE0 for approximately two bit times,

followed by J for one bit time. The transceiver drives a J state for one bit time following the SE0 to complete the EOP.

The Link must wait for one bit time following line state indication of the SE0 to J transition to allow the transceiver to

complete the one bit time J state. All bit times are relative to the speed of transmission.

In the case of Full Speed or Low Speed, after STP is asserted each FS/LS bit transition will generate a RXCMD since

the bit times are relatively slow.

FIGURE 6-9:

ULPI TRANSMIT IN SYNCHRONOUS MODE

Note:

The Link cannot assert STP with NXT de-asserted since the USB3370 is expecting to fetch another byte

from the Link.

DATA[7:0]

DP/DM

DIR

CLK

STP

NXT

TXD CMD

(USB tx)

Idle

IDLE

SE0

!SQUELCH

SE0

Turn

Around

Turn

Around

RXD

CMD

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