Chapter 12: 10/100 IEEE802.3 Media Access Controller
TX7901 User’s Manual (Rev. 6.30T – Nov, 2001)
12-47
12.5.2.3.5 Error
Conditions
The TxFIFO has the capability of stopping its operation when an error occurs. This option
can be enabled by setting the TxEnHalt bit in the transmit frame configuration register. The
following conditions cause the TxFIFO to stop: excessive deferral, excessive collisions, late
collision, or TxFIFO overrun.
When the FIFO is halted, the TxStart bit in the TFCReg is cleared and TxFrmReq is
deasserted until the condition is cleared by setting the TxStart bit in the TFCReg.
12.5.2.3.6 Enabling
The TxFIFO must be enabled before transmission starts, but after a Stop condition. This is
done by setting the Enable bit in the TFCReg.
12.5.2.3.7
Short Frame Padding
The MAC can transmit a frame of any length. If the PAD bit and CRC bit in the TFCReg are
set, MAC will automatically pad short frames to 64 bytes in length, and include CRC.
12.5.2.3.8 Multiple
Frames
The TxFIFO is capable of holding multiple frames. Frame boundaries in the FIFO are
recognized by the SOF and EOF. If there is no SOF before EOF, the data are ignored.
12.5.2.4
RxFIFO Specific Functions
The RxFIFO buffers frames as they are received from the network.
12.5.2.4.1 Multiple
Frames
The RxFIFO has the ability to hold multiple frames at any given time. If several short frames
are received before the MAC gets the G-Bus, then all of those frames will be stored.
12.5.2.4.2
Start and End of Frame
The MAC will mark the SOF and EOF in the frame Descriptor after the frame data have
been read from the RxFIFO. The frame byte length is 16 bits. If a frame is larger than 64 KB,
the length is represented as FFFFH.
12.5.2.4.3
Stripping CRC from Receive Frames
The RxNoCRC bit in the RFCReg determines whether or not the CRC is removed from each
incoming frame. If RxNoCRC is low, the CRC is not stripped.
12.5.2.4.4 Receive
Statistics
The status bits are recorded in two places as frames are received. First, a Receive
Diagnostic Register (RDReg) is updated at the end of every receive frame. It is not practical
for the system to read this register after each frame is read. Instead, the contents of this
Summary of Contents for TMPR7901
Page 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Page 14: ...Handling Precautions ...
Page 15: ......
Page 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Page 41: ...4 Precautions and Usage Considerations 4 2 ...
Page 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
Page 43: ......
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Page 260: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 2 ...