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LAN8720AI 参数 Datasheet PDF下载

LAN8720AI图片预览
型号: LAN8720AI
PDF下载: 下载PDF文件 查看货源
内容描述: 小尺寸RMII 10/100以太网收发器, HP Auto-MDIX的支持 [Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support]
分类和应用: 以太网局域网(LAN)标准
文件页数/大小: 79 页 / 1119 K
品牌: SMSC [ SMSC CORPORATION ]
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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support  
Datasheet  
3.1.2.3  
3.1.2.4  
NRZI and MLT-3 Decoding  
The DSP generates the MLT-3 recovered levels that are fed to the MLT-3 converter. The MLT-3 is then  
converted to an NRZI data stream.  
Descrambling  
The descrambler performs an inverse function to the scrambler in the transmitter and also performs  
the Serial In Parallel Out (SIPO) conversion of the data.  
During reception of IDLE (/I/) symbols. the descrambler synchronizes its descrambler key to the  
incoming stream. Once synchronization is achieved, the descrambler locks on this key and is able to  
descramble incoming data.  
Special logic in the descrambler ensures synchronization with the remote transceiver by searching for  
IDLE symbols within a window of 4000 bytes (40us). This window ensures that a maximum packet size  
of 1514 bytes, allowed by the IEEE 802.3 standard, can be received with no interference. If no IDLE-  
symbols are detected within this time-period, receive operation is aborted and the descrambler re-starts  
the synchronization process.  
3.1.2.5  
3.1.2.6  
Alignment  
The de-scrambled signal is then aligned into 5-bit code-groups by recognizing the /J/K/ Start-of-Stream  
Delimiter (SSD) pair at the start of a packet. Once the code-word alignment is determined, it is stored  
and utilized until the next start of frame.  
5B/4B Decoding  
The 5-bit code-groups are translated into 4-bit data nibbles according to the 4B/5B table. The  
translated data is presented on the RXD[1:0] signal lines. The SSD, /J/K/, is translated to “0101 0101”  
as the first 2 nibbles of the MAC preamble. Reception of the SSD causes the transceiver to assert the  
receive data valid signal, indicating that valid data is available on the RXD bus. Successive valid code-  
groups are translated to data nibbles. Reception of either the End of Stream Delimiter (ESD) consisting  
of the /T/R/ symbols, or at least two /I/ symbols causes the transceiver to de-assert the carrier sense  
and receive data valid signals.  
Note: These symbols are not translated into data.  
3.1.2.7  
Receive Data Valid Signal  
The Receive Data Valid signal (RXDV) indicates that recovered and decoded nibbles are being  
presented on the RXD[1:0] outputs synchronous to RXCLK. RXDV becomes active after the /J/K/  
delimiter has been recognized and RXD is aligned to nibble boundaries. It remains active until either  
the /T/R/ delimiter is recognized or link test indicates failure or SIGDET becomes false.  
RXDV is asserted when the first nibble of translated /J/K/ is ready for transfer over the Media  
Independent Interface (MII mode).  
J
K
5
5
5
D
Idle  
data data data data  
T
R
CLEAR-TEXT  
RX_CLK  
RX_DV  
5
5
5
5
5
D
data data data data  
RXD  
Figure 3.3 Relationship Between Received Data and Specific MII Signals  
SMSC LAN8720A/LAN8720Ai  
21  
Revision 1.4 (08-23-12)  
DATASHEET