MPC8280 datasheet(842/1386 Pages) FREESCALE

842 / 1386 page

Universal Serial Bus Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

27-26

Freescale Semiconductor

The receive buffer pointer always points to the first location of the associated buffer. The pointer must be

divisible by 4. The buffer may reside in either internal or external memory.

27.6.2

USB Transmit Buffer Descriptor (Tx BD) for Function

Data that the USB function wishes to transmit to the host is arranged in buffers referenced by the Tx BD

ring. The first word of the Tx BD contains the status and control bits.

Table 27-17 describes USB TxBD fields.

012

34567

OFFSET + 0

—

CNF

PID

—TO

—

OFFSET + 2

DATA LENGTH

OFFSET + 4

TX DATA BUFFER POINTER

OFFSET + 6

Figure 27-19. USB Transmit Buffer Descriptor (Tx BD)1,2

1 Entries in boldface must be initialized by the user.

2 All fields should be prepared by the user before transmission.

Table 27-17. USB Function Tx BD Fields

Offset

Bit

Name

Description

0x00

Ready

0 The data buffer associated with this BD is not ready for transmission. The user is

free to manipulate this BD or its associated data buffer. The CP clears this bit after

the buffer has been transmitted or after an error condition is encountered.

1 The data buffer, which has been prepared for transmission by the user, has not

been transmitted or is currently being transmitted. No fields of this BD may be

written by the user once this bit is set.

—

Reserved, should be cleared

Wrap (Final BD in table)

0 This is not the last BD in the Tx BD table.

1 This is the last BD in the Tx BD table. After this buffer has been used, the CP will

send data using the first BD in the table (the BD pointed to by TBASEx). The

number of Tx BDs in this table is programmable, and is determined only by the Tx

BD[W] and the overall space constraints of the dual-port RAM.

Interrupt

0 No interrupt is generated after this buffer has been serviced.

1The TXB or TXE bit in the event register is set when this buffer is serviced. TXB and

TXE can cause interrupts if they are enabled.

Last

0 Buffer does not contain the last byte of the message

1 Buffer contains the last byte of the message

Transmit CRC. Valid only when the L bit is set; otherwise it is ignored. Prepare TC

before sending data.

0 Transmit end-of-packet after the last data byte. This setting can be used for testing

purposes to send a bad CRC after the data.

1 Transmit the CRC sequence after the last data byte.

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