USB3300 datasheet(25/53 Pages) MICROCHIP

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DS00001783B-page 25

USB3300

6.1.5.1

ULPI Register Write

A ULPI register write operation is given in Figure 6-4. The TXD command with a register write DATA[7:6] = 10b is driven

by the Link at T0. The register address is encoded into DATA[5:0] of the TXD CMD byte.

To write to a register, the Link will wait until DIR is low, and at T0, drive the TXD CMD on the databus. At T2 the PHY

will drive NXT high. On the next rising clock edge, T3, the Link will write the register data. At T4 the PHY will accept the

register data and the Link will drive an Idle on the bus and drive STP high to signal the end of the data packet. Finally,

at T5, the PHY will latch the data into the register and drive NXT low. The Link will pull STP low.

NXT is used to control when the Link drives the register data on the bus. DIR is low throughout this transaction since

the PHY is receiving data from the Link. STP is used to end the transaction and data is registered after the de-assertion

of STP. After the write operation completes, the Link must drive a ULPI Idle (00h) on the data bus or the USB3300 may

decode the bus value as a ULPI command.

FIGURE 6-4:

ULPI REGISTER WRITE

DIR

CLK

DATA[7:0]

STP

NXT

TXD CMD

(reg write)

Idle

Reg Data[n]

Idle

ULPI Register

Reg Data [n-1]

Reg Data [n]

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