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CS8900A-IQ 参数 Datasheet PDF下载

CS8900A-IQ图片预览
型号: CS8900A-IQ
PDF下载: 下载PDF文件 查看货源
内容描述: 水晶局域网? ISA以太网控制器 [Crystal LAN ⑩ ISA Ethernet Controller]
分类和应用: 控制器局域网以太网
文件页数/大小: 128 页 / 1360 K
品牌: CIRRUS [ CIRRUS LOGIC ]
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CS8900A  
Crystal LAN™ ISA Ethernet Controller  
3.11.2 Transmitter  
are tested by the squelch circuit. Any signal with  
amplitude less than the squelch threshold (either  
positive or negative, depending on polarity) is re-  
jected.  
When configured for 10BASE-T operation,  
Manchester encoded data from the ENDEC is fed  
into the transmitter’s predistortion circuit where  
initial wave shaping and preequalization is per-  
formed. The output of the predistortion circuit is  
fed into the transmit filter where final wave shaping  
occurs and unwanted noise is removed. The signal  
then passes to the differential driver where it is am-  
plified and driven out of the TXD+/TXD- pins.  
3.11.3.2 Extended Range  
The CS8900A supports an Extended Range feature  
that reduces the 10BASE-T receive squelch thresh-  
old by approximately 6 dB. This allows the  
CS8900A to operate with 10BASE-T cables that  
are longer than 100 meters (100 meters is the max-  
imum length specified by the Ethernet standard).  
The exact additional distance depends on the qual-  
ity of the cable and the amount of electromagnetic  
noise in the surrounding environment. To activate  
this feature, the host must set the LoRxSquelch bit  
(Register 13, LineCTL, Bit E).  
In the absence of transmit packets, the transmitter  
generates link pulses in accordance with section  
14.2.1.1. of the Ethernet standard. Transmitted link  
pulses are positive pulses, one bit time wide, typi-  
cally generated at a rate of one every 16 ms. The  
16 ms timer starts whenever the transmitter com-  
pletes an End-of-Frame (EOF) sequence. Thus,  
there is a link pulse 16 ms after an EOF unless there  
is another transmitted packet. Figure 14 diagrams  
the operation of the Link Pulse Generator.  
3.11.4 Link Pulse Detection  
To prevent disruption of network operation due to  
a faulty link segment, the CS8900A continually  
monitors the 10BASE-T receive pair (RXD+/  
RXD-) for packets and link pulses. After each  
packet or link pulse is received, an internal Link-  
Loss timer is started. As long as a packet or link  
pulse is received before the Link-Loss timer finish-  
es (between 25 and 150 ms), the CS8900A main-  
tains normal operation. If no receive activity is  
detected, the CS8900A disables packet transmis-  
sion to prevent "blind" transmissions onto the net-  
work (link pulses are still sent while packet  
transmission is disabled). To reactivate transmis-  
sion, the receiver must detect a single packet (the  
packet itself is ignored), or two link pulses separat-  
If no link pulses are being received on the receiver,  
the 10BASE-T transmitter is internally forced to an  
inactive state unless bit DisableLT in register 19  
(Test Control register) is set to one.  
3.11.3 Receiver  
The 10BASE-T receive section consists of the re-  
ceive filter, squelch circuit, polarity detection and  
correction circuit, and link pulse detector.  
3.11.3.1 Squelch Circuit  
The 10BASE-T squelch circuit determines when  
valid data is present on the RXD+/RXD- pair. In-  
coming signals passing through the receive filter  
Time  
Link  
Link  
Pulse  
Pulse  
Packet  
Packet  
Less Than  
16ms  
16ms  
16ms  
Figure 14. Link Pulse Transmission  
CIRRUS LOGIC PRODUCT DATA SHEET  
36  
DS271PP3  
 
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