USB334X datasheet(54/92 Pages) MICROCHIP

54 / 92 page

USB334x

DS00002646A-page 54

 2009-2018 Microchip Technology Inc.

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 USB334x 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 USB334x 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.

6.4.2.1

Link Power Management Token Transmit

A Host Link can send a LPM command using the USB334x. When sending the LPM token the normal transmit method

is not used. Sending a LPM token requires the USB334x to send a 0000b or ‘F0’ PID. When the ULPI specification was

defined the ‘F0’ PID was not defined. The ULPI specification used the “Reserved” ‘F0’ PID to signal chirp and resume

signaling while using OpMode 10b. While in OpMode 00b the USB334x is able to generate the ‘F0’ PID as shown below.

FIGURE 6-9:

ULPI TRANSMIT IN SYNCHRONOUS MODE

Note:

The Link cannot assert STP with NXT de-asserted since the USB334x 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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