Chapter 12: 10/100 IEEE802.3 Media Access Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
12-10
Bit(s)
Field
R/W
Description
the PHY. When TxSQE is 1, the transmitter reports the status of SQE test.
This bit should be 0 if the 100Base-X or 100Base-T PHY being used does not perform the
SQE test.
25:24
–
R/O
Reserved
23:16
TxSOFTh
[7:0]
R/W
Transmit Start of Frame Threshold (0000_1000)
This threshold indicates how many 8-byte units should be written to the Tx_FIFO before a
transmit attempt is initiated. This is the minimum requirement to start the frame
transmission. If the frame size is less than the TxSFTH, the transmission starts after EOF.
15
HwDupSelEn
R/W
Hardware Full Duplex Select Enable (0)
When set, the macxHwFDupSel input pin overrides the setting of the FDup register bit.
When reset, the macxHwFDupSel pin is ignored.
14
FDup
R/W
Full-Duplex (0)
When set, the port is in the full-duplex mode so that frames can be transmitted and
received at the same time. In the full-duplex mode, the transmitter ignores receive carrier
and collision indications before and during transmission. When reset, the port works in the
half-duplex mode.
13
LoopEn
RW
Loopback Enable (0)
The MAC can be configured for loop-back diagnostic operation by setting this bit.
12
LoopSel
R/W
Loop-back Select (0)
When set, Loop-back allows transmitted data to be looped back through the TxFIFO and
RxFIFO to test DMA and FIFO circuitry. If it is zero, the loop-back goes deeper, including
the MAC block. In both situations, data are not transmitted on the MII. Loop-back is only
possible in the full-duplex mode.
11
TxEnCRCSel
R/W
Transmit CRC Enable Select (0)
When set, TxEnCRC bit is overridden by TxEnCRCDes.
10
TxEnCRC
R/W
Transmit CRC Enable (0)
While CRC is low, the CRC check sum is neither calculated nor appended to each
transmitted frame.
9
TxEnPad
R/W
Pad Transmit Data (0)
While this bit is set, the MAC will automatically append data to a frame less than 60 bytes
in length. The TxEnCRC bit should be set also, so a valid CRC is appended to the frame.
Otherwise, the frame will be transmitted with a bad CRC. If this bit is reset and a frame
less than 60 bytes in length is written to the TxFIFO, this frame is transmitted unchanged.
8
TxEnHalt
R/W
Halt on Error Condition (1)
When this bit is set, the TxFIFO will halt after error conditions such as TxFIFO overflow,
late collision, excessive deferral, or excessive collision.
Resetting the TxStart bit in this register restarts the TxFIFO.
7:6
TxRetrySel
[1:0]
R/W
Retry Attempt Select (00)
These bits set the number of attempts the transmitter makes to transmit a frame. After this
number of attempts, the transmitter aborts the transmission of the frame, resulting in an
excessive collision error.
Retry[1:0] Transmit Attempts
00 16 (default)
01 8
10 4
11 1
5
TxBOffSel
R/W
Back-off Select (0)
When this bit is set, the transmitter will only wait 96 bit times before re-transmitting a frame
after a collision. When it is 0, a random backoff time is calculated. The random number of
slot times is calculated based on the following algorithm:
T = 512
×
R (bit times)
0
≤
R
≤
2 ^ (min (n,10))
and n is the number of collisions that have occurred for the current transmit attempt.
4
TxAbDefer
R/W
Abort After Max Deferral (0)
When this bit is set, the transmitter aborts a transmission if it is deferring for more than
24,288 bit times.
3:2
TxPreAmSel
[1:0]
R/W
Transmit Preamble Length Select (00)
These bits must remain zero in order to append a 7-byte preamble and a 1-byte start of
frame delimiter to the frame data. Values other than zero are reserved, and should not try
Содержание TMPR7901
Страница 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Страница 14: ...Handling Precautions ...
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Страница 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Страница 41: ...4 Precautions and Usage Considerations 4 2 ...
Страница 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
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Страница 259: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 1 13 Removed ...
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