USB334X datasheet(45/92 Pages) MICROCHIP

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DS00002646A-page 45

USB334x

6.2.2

ULPI REGISTER WRITE

A ULPI register write operation is given in Figure 6-3. The TX 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 TX CMD byte.

To write a register, the Link will wait until DIR is low, and at T0, drive the TX CMD on the data bus. 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

packet. Finally, at T5, the PHY will latch the data into the register and the Link will pull STP low.

TABLE 6-2:

ULPI TX CMD BYTE ENCODING

Command Name

CMD Bits[7:6]

CMD Bits[5:0]

Command Description

Idle

00b

000000b

ULPI Idle

Transmit

01b

000000b

USB Transmit Packet with No Packet Identifier

(NOPID)

00XXXXb

USB Transmit Packet Identifier (PID) where DATA[3:0]

is equal to the 4-bit PID. P3P2P1P0 where P3 is the

MSB.

10b

XXXXXXb

Immediate Register Write Command where:

DATA[5:0] = 6-bit register address

101111b

Extended Register Write Command where the 8-bit

11b

XXXXXXb

Immediate Register Read Command where:

DATA[5:0] = 6-bit register address

101111b

Extended Register Read Command where the 8-bit

FIGURE 6-3:

ULPI REGISTER WRITE IN SYNCHRONOUS MODE

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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