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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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MU9C8338 10/100Mb Ethernet Filter Interface  
Functional Description  
LANCAM Sequencer  
Aging and Purging  
The sequencer is a state machine that generates the control  
signals required for CAM read and write cycles, and  
multiplexes appropriate data and operational codes to  
LANCAM data lines. The sequencer operations are:  
Time stamps are added automatically to the LANCAM  
entries by the MU9C8338. Two counters are provided to  
store the current and purge time stamps. The Current Time  
Stamp is the 8-bit value that automatically is added or  
updated when a SA processing function is completed. The  
Purge Time stamp is the 8-bit value that is compared with  
the 8-bit time stamps stored with the LANCAM entries  
during purges. The initial value of the counters are  
STPURG = 01H and STCURR = 00H. The counters may  
be incremented individually through the CPU commands.  
Either the CPU or the external INCR pin can increment  
both counters simultaneously. Whenever STPURG is  
incremented, a purge operation is initiated. The counters  
roll-over so the times should be thought of as slots to be  
used and reused in a round-robin fashion.  
Execute LANCAM cycles for CPU port  
DA processing  
SA processing  
Purging of aged entries  
Add Permanent Entries to LANCAM database  
Delete Entries from LANCAM database  
Read Entries from the LANCAM database.  
FIFO and Result Port  
When the DA sequence is executed, the result is stored in  
a FIFO for later collection by either the CPU over the  
Processor Bus from the Result register, or by external  
hardware attached to the Result port.  
The existence of two counters (time stamps) allows the  
data-aging rate to be varied according to network traffic  
density. When the difference between the counters is large  
(default), the address data is purged less frequently;  
shrinking the counter difference causes the data to age  
sooner. Incoming SAs are time stamped or updated with  
the current value of STCURR. Older entries time stamped  
with the same value as STPURG are purged upon the  
increment of STPURG. The permanent address database  
built using the Add routine is not affected by time stamps.  
Initialization  
At power-up or after a hardware reset, the host processor  
should download the LANCAM configuration and register  
contents to enable the LANCAM to operate as required.  
The LANCAM initialization and configuration that is  
downloaded by the CPU should do the following: The  
individual Page Address registers of each LANCAM in  
the LANCAM chain should be set with appropriate values.  
The Foreground Register set should be set to allow normal  
DA and SA filtering. This involves setting the Control,  
Segment Control, and Mask registers to suit. The  
Background Register set should be set to allow the  
background management tasks to be preformed. This  
involves setting the Control, Segment Control, and Mask  
registers to suit. The LANCAM should be configured to  
store 48-bit MAC addresses in segments 3–1 and the  
associated data in segment 0. The allocation of bits in the  
16-bit associated data segment is specified in the  
description of the SCDW0 Association Data register.  
The data age gap is effectively the length of time an entry  
will exist in the LANCAM database if it is not updated.  
This gap is the difference between the STCURR and  
STPURG counter. When network traffic is low, STCURR  
may be increased in order to increase the length of time an  
entry will exist. When network traffic is high, STPURG  
may be increased in order to decrease the length of time an  
entry will exist. When STPURG is incremented older  
entries are also purged from the database if their time  
stamp matches STPURG.  
STCURR and STPURG may be incremented  
simultaneously to keep the data age gap constant and to  
purge the older entries from the database.  
Permanent Station Addresses  
To maintain "current" time, STCURR is advanced in any  
one of the three ways:  
Using the Add Entry routine, the nonvolatile station list  
can be added to the LANCAM by the host processor. The  
Associated Data bit 15 is set to 1, to indicate a permanent  
entry. Permanent entries are removed only with the Delete  
Entry routine.  
1. The CPU issues an increment STCURR command.  
Only the STCURR counter is increased.  
2. The CPU issues an increment STCURR and STPURG  
command. Both counters are increased simultaneously.  
Management  
The Delete Entry and Read Entry routines are available for  
database maintenance and housekeeping. Although  
permanent addresses cannot be purged, they can be deleted  
using the management Delete Entry routine.  
3. The INCR pin is asserted. Both counters are increased  
simultaneously.  
To maintain "purge" time and to purge aged CAM entries,  
STPURG is advanced in any one of the following three  
ways:  
10  
Rev. 1a  
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