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Ethernet Module
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
Freescale Semiconductor
11-21
11.5.11 Transmit FIFO Watermark (TFWR)
The TFWR register, shown in
, controls the amount of data required in the transmit FIFO
before transmission of a frame can begin. Setting TFWR to larger values reduces the risk of transmit FIFO
underrun due to system bus latency.
31
16
Field
—
Reset
0000_0000_0000_0000
R/W
Read/Write
15
2
1
0
Field
—
X_WMRK
Reset
0000_0000_0000_00
00
R/W
Read/Write
Addr
MBAR + 0x8E4
Figure 11-15. Transmit FIFO Watermark (TFWR)
Table 11-18. TFWR Field Descriptions
Bits
Name
Description
31–2
—
Reserved, should be cleared.
1–0
X_WMRK
Transmit FIFO watermark. Frame transmission begins when the number of bytes selected by this
field are written into the transmit FIFO, if an end of frame has been written to the FIFO, or if the
FIFO is full before the selected number of bytes are written. The options are:
0X 64 bytes written to transmit FIFO
10 128 bytes written to transmit FIFO
11 192 bytes written to transmit FIFO