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CS8900A 参数 Datasheet PDF下载

CS8900A图片预览
型号: CS8900A
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  
1.6 µs after the end of transmission. During this pe- routed to either the 10BASE-T transceiver or AUI,  
riod, the CS8900A ignores receive carrier activity  
(see SQE Error in this section for more informa-  
tion).  
depending on configuration.  
3.10.2 Carrier Detection  
The internal Carrier Detection circuit informs the  
MAC that valid receive data is present by asserting  
the internal Carrier Sense signal as soon it detects a  
valid bit pattern (1010b or 0101b for 10BASE-T,  
and 1b or 0b for AUI). During normal packet recep-  
tion, Carrier Sense remains asserted while the  
frame is being received, and is deasserted 1.3 to 2.3  
bit times after the last low-to-high transition of the  
End-of-Frame (EOF) sequence. Whenever the re-  
ceiver is idle (no receive activity), Carrier Sense is  
deasserted. The CRS bit (Register 14, LineST,  
Bit E) reports the state of the Carrier Sense signal.  
3.10 Encoder/Decoder (ENDEC)  
The CS8900A’s integrated encoder/decoder (EN-  
DEC) circuit is compliant with the relevant por-  
tions of section 7 of the Ethernet standard (ISO/IEC  
8802-3, 1993). Its primary functions include:  
Manchester encoding of transmit data; informing  
the MAC when valid receive data is present (Carri-  
er Detection); and, recovering the clock and NRZ  
data from incoming Manchester-encoded data.  
Figure 12 provides a block diagram of the ENDEC  
and how it interfaces to the MAC, AUI and  
10BASE-T transceiver.  
3.10.3 Clock and Data Recovery  
When the receiver is idle, the phase-lock loop  
(PLL) is locked to the internal clock signal. The as-  
sertion of the Carrier Sense signal interrupts the  
PLL. When it restarts, it locks on the incoming da-  
ta. The receive clock is then compared to the in-  
coming data at the bit cell center and any phase  
difference is corrected. The PLL remains locked as  
long as the receiver input signal is valid. Once the  
PLL has locked on the incoming data, the ENDEC  
converts the Manchester data to NRZ and passes  
the decoded data and the recovered clock to the  
MAC for further processing.  
3.10.1 Encoder  
The encoder converts NRZ data from the MAC and  
a 20 MHz Transmit Clock signal into a serial  
stream of Manchester data. The Transmit Clock is  
produced by an on-chip oscillator circuit that is  
driven by either an external 20 MHz quartz crystal  
or a TTL-level CMOS clock input. If a CMOS in-  
put is used, the clock should be 20 MHz ±0.01%  
with a duty cycle between 40% and 60%. The spec-  
ifications for the crystal are described in  
Section 7.7 on page 121. The encoded signal is  
ENDEC  
RXSQL  
Carrier  
Carrier Sense  
Detector  
10BASE-T  
Transceiver  
RX  
TX  
RX CLK  
Decoder  
RX  
MUX  
& PLL  
RX NRZ  
MAC  
AUISQL  
AUIRX  
TXCLK  
TX NRZ  
Encoder  
TX  
TEN  
MUX  
AUITX  
AUICol  
AUI  
Port Select  
Collision  
Clock  
Figure 12. ENDEC  
CIRRUS LOGIC PRODUCT DATA SHEET  
34  
DS271PP3