26
Agere Systems Inc.
Data Sheet, Rev. 4
June 2001
USB Device Controller
USS-820D
Register Interface
(continued)
Table 21. Function Address Register (FADDR)—Address: 10H; Default: 0000 0000B
This SFR holds the address for the USB function. During bus enumeration, it is written by firmware with a unique
value assigned by the host. If MCSR.FEAT = 1, this register is reset to 0 if a USB reset is detected.
Table 22. Transmit FIFO Data Register (TXDAT)—Address: 00H; Default: 0000 0000B
Data to be transmitted by the FIFO specified by EPINDEX is first written to this register. This register is endpoint
indexed. TXDAT must not be written if TXFIF = 11.
Table 23. Transmit FIFO Byte-Count High and Low Registers (TXCNTH, TXCNTL)—Address:
TXCNTH = 02H, TXCNTL = 01H; Default: TXCNTH = 0000 0000B; TXCNTL = 0000 0000B
Written by firmware to indicate the number of bytes just written to the transmit FIFO specified by EPINDEX. This
register is endpoint indexed. TXCNTL should be written after TXCNTH. TXCNTL write increments TXFIF, vali-
dating the data set just written.
Note: To send a status stage after a control write, no data control command, or a null packet, write 0 to TXCNT.
Bit 7
—
—
Bit 6
A6
Bit 5
A5
Bit 4
A4
Bit 3
A3
R/W
Bit 2
A2
Bit 1
A1
Bit 0
A0
Bit
7
6:0
Symbol
—
A[6:0]
Function/Description
Reserved.
Write 0 to this bit. Reads always return 0.
7-Bit Programmable Function Address.
This register is written by firmware as a
result of commands received via endpoint 0.
Bit 7
TXDAT7
Bit 6
TXDAT6
Bit 5
TXDAT5
Bit 4
TXDAT4
Bit 3
TXDAT3
Bit 2
TXDAT2
Bit 1
TXDAT1
Bit 0
TXDAT0
W
Bit
7:0
Symbol
TXDAT[7:0
]
Function/Description
Transmit Data Byte (Write Only).
To write data to the transmit FIFO, write to this
register. The write pointer is incremented automatically after a write.
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
BC9
Bit 8
BC8
—
—
R/W
Bit 7
BC7
Bit 6
BC6
Bit 5
BC5
Bit 4
BC4
Bit 3
BC3
Bit 2
BC2
Bit 1
BC1
Bit 0
BC0
R/W
Bit
15:10
9:0
Symbol
—
BC[9:0]
Function/Description
Reserved.
Write 0s to these bits. Reads always return 0s.
Transmit Byte Count (Write, Conditional Read).
10-bit, ring buffer. These bits store
transmit byte count (TXCNT).