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ETHERNET Controller
MOTOROLA
MC68EN302 REFERENCE MANUAL
4-17
W—Wrap (Final BD in Table), written by user.
0 = This is not the last buffer descriptor in the Tx BD table.
1 = This is the last buffer descriptor in the Tx BD table. After this buffer has been used,
the Ethernet controller transmits data from the first BD in the table. The maximum
number of Tx BDs in this table is programmable through the BDSIZE bits.
I—Interrupt, written by user.
0 = No interrupt is generated after this buffer has been serviced.
1 = TBINT is set in the Ethernet event register after this buffer has been serviced. If
enabled through the mask register, this bit can cause interrupts to the host.
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.
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.
DEF—Defer Indication, written by Ethernet controller (only valid if L = 1).
The Ethernet controller had to defer while attempting frame transmission. DEF is not set if
a collision occurs during transmission.
HB—Heartbeat Error, written by Ethernet controller (only valid if L = 1).
The collision input was not asserted within the heartbeat window after transmit completion.
HB may be set only if HBC is not set in the ECNFIG register.
LC—Late Collision, written by Ethernet controller (only valid if L = 1).
A collision has occurred after 56 data bytes have been transmitted. The Ethernet controller
terminates the transmission.
RL—Retransmission Limit, written by Ethernet controller (only valid if L = 1).
The transmitter has failed (Retry Limit + 1) attempts to successfully transmit a message due
to repeated collisions on the medium.
RC—Retry Count, written by Ethernet controller (only valid if L = 1).
These four bits indicate the number of retries required before this frame was successfully
transmitted. If RC = 0, then the frame was transmitted correctly the first time. If RC = 15,
then the frame was transmitted successfully while the retry count was at its maximum value.
If RL is set, then RC has no meaning.
UN—Underrun, written by Ethernet controller (only valid if L = 1).
A transmit FIFO underrun occurred while transmitting one or more of the the data buffers
associated with this frame. When FIFO underrun occurs, frame transmission halts once an
incorrect CRC is appended. The remaining buffer(s) associated with this frame are DMA’d
and dumped by the transmit logic.