Microcontroller User's Manual

17-50 MCF5282 User’s Manual MOTOROLA
Buffer Descriptors
Figure 17-28. Transmit Buffer Descriptor (TxBD)
Table 17-37. Transmit Buffer Descriptor Field Definitions
Word Location Field Name Description
Offset + 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
once this bit is set.
Offset + 0 Bit 14 TO1 Transmit software ownership. This field is reserved for software
use. This read/write bit will not be modified by hardware, nor will
its value affect hardware.
Offset + 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.
Offset + 0 BIt 12 TO2 Transmit software ownership. This field is reserved for use by
software. This read/write bit will not be modified by hardware,
nor will its value affect hardware.
Offset + 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.
Offset + 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.
Offset + 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).
Offset + 0 Bits [8:0] — Reserved.
Offset + 0
Offset + 2
Offset + 4
Offset + 6
Tx Data Buffer Pointer - A[15:0]
Data Length
TCLTO2WTO1R ABC
Tx Data Buffer Pointer - A[31:16]
0123456789101112131415