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COM20020-5 参数 Datasheet PDF下载

COM20020-5图片预览
型号: COM20020-5
PDF下载: 下载PDF文件 查看货源
内容描述: 通用局域网控制器2K ×8板载RAM [Universal Local Area Network Controller with 2K x 8 On-Board RAM]
分类和应用: 控制器局域网
文件页数/大小: 58 页 / 248 K
品牌: SMSC [ SMSC CORPORATION ]
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one obtains the contents of COM20020-5  
internal RAM. Performing only read from the  
Data Register does not load a new data from the  
The Backplane Configuration provides for direct  
connection between the COM20020-5 and the  
media. Only one pull-up resistor  
(in open drain  
During a write operation, the data  
is required  
internal RAM.  
configuration of the output driver)  
is stored in the data register and then written  
into memory. Whenever the pointer is loaded for  
reads with a new value, data is immediately  
prefetched to prepare for the first read operation.  
somewhere on the media (not on each  
individual node). The nPULSE1 signal, in this  
mode, is an open drain or push/pull driver and is  
used to directly drive the media. It issues a  
100nS negative pulse to transmit a logic "1".  
Note that when used in the open-drain mode,  
the COM20020-5 does not have a fail/safe input  
on the RXIN pin.  
TRANSMISSION MEDIA INTERFACE  
The bottom half of Figure 2 illustrates the  
COM20020-5 interface to the transmission  
media used to connect the node to the network.  
The user may interface to the cable of choice in  
one of two ways:  
The nPULSE1 signal actually contains a weak  
pull-up resistor. This pull-up should not take the  
place of the resistor required on the media for  
open drain mode. In typical applications, the  
serial backplane is terminated at both ends and  
a bias is provided by the external pull-up  
resistor.  
Backplane Configuration  
The Backplane Configuration is recommended  
for cost-sensitive, short-distance applications  
like backplanes and instrumentation. This mode  
is advantageous because it saves components,  
cost, and power.  
The RXIN signal is directly connected to the  
cable via an internal Schmitt trigger. A negative  
pulse on this input indicates a logic "1". Lack of  
pulse indicates a logic "0". For typical single-  
ended backplane applications, RXIN is  
connected to nPULSE1 to make the serial  
backplane data line. A ground line (from the  
coax or twisted pair) should run in parallel with  
the signal. For applications requiring different  
treatment of the receive signal (like filtering or  
squelching), nPULSE1 and RXIN remain as  
Since the Backplane Configuration encodes data  
differently  
than  
the  
traditional  
Hybrid  
Configuration, nodes utilizing the Backplane  
Configuration cannot communicate directly with  
nodes  
utilizing  
the  
Traditional  
Hybrid  
Configuration.  
The Backplane Configuration does not isolate  
the node from the media nor protects it from  
Common Mode noise, but Common Mode Noise  
is less of a problem in short distances.  
independent pins.  
External differential  
drivers/receivers for increased range and  
common mode noise rejection, for example,  
would require the signals to be independent of  
one another. When the device is in Backplane  
Mode, the clock provided by the nPULSE2  
signal may be used for encoding the data into a  
different encoding scheme or other synchronous  
operations needed on the serial data stream.  
The COM20020-5 supplies a programmable  
output driver for Backplane Mode operation. A  
push/pull or open drain driver can be selected by  
programming the P1MODE bit of the Setup  
Register (see register descriptions for details.)  
The COM20020-5 defaults to an open drain  
output.  
Differential Driver Configuration  
The Differential Driver Configuration is a special  
case of the Backplane Mode. It is a dc coupled  
15