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MU9C8338 参数 Datasheet PDF下载

MU9C8338图片预览
型号: MU9C8338
PDF下载: 下载PDF文件 查看货源
内容描述: 10 / 100Mb的以太网接口筛选 [10/ 100Mb Ethernet Filter Interface]
分类和应用: 以太网
文件页数/大小: 28 页 / 428 K
品牌: MUSIC [ MUSIC SEMICONDUCTORS ]
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Functional Description  
MU9C8338 10/100Mb Ethernet Filter Interface  
1. The CPU issues an increment STPURG command.  
Only the STPURG counter is increased.  
purged automatically without further involvement.  
If the C AM Full flag is asserted, an interrupt (if  
2. The CPU issues an increment STCURR and STPURG  
command. Both counters are increased simultaneously.  
configured) to the CPU is generated. Assume that  
STCURR = F0H, and STPURG = F1H. The CPU may  
initiate an increment STPURG operation so that older  
entries may be purged. This increases the value of  
STPURG to F2H. A purge operation is initiated that will  
eliminate all CAM entries with time stamp = F2H.  
3. The INCR pin is asserted. Both counters are increased  
simultaneously.  
If the STPURG value was incremented, the MU9C8338  
initiates a purge operation using the new STPURG value.  
STPURG should never be incremented to equal STCURR.  
The CPU should monitor the System Status register, and if  
the CAM is still full, the operation can be repeated until  
entries are purged and the CAM Full flag is de-asserted.  
The time stamping of LANCAM entries and the procedure  
required to initiate a purge is explained as follows:  
Assume that STPURG was incremented 128 times. This  
would purge the oldest half of the time stamp values and  
thus, reduce the maximum age to half the previous 255.  
This can be accomplished without disturbing ongoing  
normal increment time stamp update operations.  
1. Incoming SAs to be learned are associated with the  
most recent STCURR value. The time stamps of each  
SA already in the CAM database is updated to  
STCURR, each time a packet with that SA is processed.  
2. STPURG and STCURR are advanced as described  
earlier to purge entries that have the same time stamp  
value as STCURR.  
CRC and Other Data Integrity Checks  
For 10Base-X packets, a 32-bit cyclic redundancy check is  
calculated from the data frame (exclusive of the preamble  
and start frame delimiter) and compared to the frame  
check sequence (FCS). This check is only performed if the  
PCFG register is set accordingly to enable the facility.  
Following is an example, beginning with the defaults,  
initially, STCURR = 00H and STPURG = 01H. As  
packets arrive, learned or refreshed, SAs are labeled with  
STCURR = 00H. (At that moment STPURG = 01H).  
Increment, either hardware or software initiated, results in  
STCURR = 01H and STPURG=02H.  
Also, according to the MII interface specifications, the  
RX_ER, CRS, and COL signals are monitored and error  
conditions are recognized. If any error is identified, the  
source address is not processed. This is intended to  
maintain the integrity of the LANCAM database.  
A purge operation is initiated that will eliminate all CAM  
entries with time stamp = 02H. The oldest entries (SAs)  
that have not been updated in 255 increment times are  
Rev. 1a  
11  
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