mcf5272 Freescale Semiconductor, Inc, mcf5272 Datasheet - Page 259

• Manufacturer Part Number: mcf5272
• Description: Mcf5272 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

MOTOROLA
The TxBD fields are detailed in Table 11-35.
Bits
5–2
15
14
13
12
11
10
9
8
7
6
1
0
Name
DEF
CSL
TO1
TO2
TC
HB
RC
UN
LC
RL
W
R
L
Ready. Written by the FEC (= 0) and user (= 1).
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.
Transmit software ownership bit.Reserved for use by software. This read/write bit is not
modified by hardware, nor does its value affect hardware.
Wrap. Written by the 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.
Transmit software ownership bit. Reserved for use by software. This read/write bit is not
modified by hardware, nor does its value affect hardware.
Last in frame. Written by the user.
0 The buffer is not the last in the transmit frame.
1 The buffer is the last in the transmit frame.
Tx CRC. Written by the user and is only valid if L = 1.
0 End transmission immediately after the last data byte.
1 Transmit the CRC sequence after the last data byte.
Defer indication. Written by the FEC and is only valid if L = 1. The FEC had to defer while
trying to transmit a frame. This bit is not set if a collision occurs during transmission.
Heartbeat error. Written by the FEC and is valid only if L = 1. The collision input was not
asserted within the heartbeat window following the completion of transmission. Cannot be
set unless the HBC bit is set in the TCR register.
Late collision. Written by the FEC and is only valid if L = 1. A collision has occurred after 56
data bytes are transmitted. The FEC terminates the transmission.
Retransmission limit. Written by the FEC and is 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.
Retry count. Written by the FEC and is valid only if L = 1. These four bits indicate the
number of retries required before this frame is 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.
Underrun. Written by the FEC and is only valid if L = 1. The FEC encountered a transmit
FIFO underrun while transmitting one or more of the data buffers associated with this
frame. When transmit FIFO underrun occurs, transmission of the frame stops, and an
incorrect CRC is appended. The remaining buffer(s) associated with this frame are sent as
a DMA and dumped by the transmit logic.
Carrier sense lost. Written by the FEC and is valid only if L = 1. Carrier sense dropped out
or never asserted during transmission of a frame without collision.
Table 11-35. TxBD Field Descriptions
Chapter 11. Ethernet Module
Description
Buffer Descriptors
11-35