Fast Ethernet Controller (FEC)
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
18-51
Figure 18-28. Transmit Buffer Descriptor (TxBD)
Table 18-37. Transmit Buffer Descriptor Field Definitions
Word
Location
Field Name
Description
0
Bit 15
R
Ready. Written by the FEC and the user.
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 FEC 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 after this bit is set.
0
Bit 14
TO1
Transmit software ownership. This field is reserved for software use. This
read/write bit is not modified by hardware nor does its value affect
hardware.
0
Bit 13
W
Wrap. Written by user.
0 The next buffer descriptor is found in the consecutive location
1 The next buffer descriptor is found at the location defined in ETDSR.
0
BIt 12
TO2
Transmit software ownership. This field is reserved for use by software.
This read/write bit is not modified by hardware nor does its value affect
hardware.
0
Bit 11
L
Last in frame. Written by user.
0 The buffer is not the last in the transmit frame.
1 The buffer is the last in the transmit frame.
0
Bit 10
TC
Tx CRC. Written by user (only valid if L = 1).
0 End transmission immediately after the last data byte.
1 Transmit the CRC sequence after the last data byte.
0
Bit 9
ABC
Append bad CRC. Written by user (only valid if L = 1).
0 No effect
1 Transmit the CRC sequence inverted after the last data byte
(regardless of TC value).
0
Bits [8:0]
—
Reserved.
2
Bits [15:0]
Data Length
Data Length, written by user.
Data length is the number of octets the FEC should transmit from this
BD’s data buffer. It is never modified by the FEC. Bits [15:5] are used by
the DMA engine, bits[4:0] are ignored.
0
2
4
6
Tx Data Buffer Pointer - A[15:0]
Data Length
TC
L
TO2
W
TO1
R
ABC
Tx Data Buffer Pointer - A[31:16]
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
