Using Motorola' Fast Static RAM CAMs on a Media Independent Interface

PublishTime：2021-11-19

●Not too long ago we were happy to have a 10 Mbps LAN connection on our desktop computer. However, given the growing popularity of the Internet and other services, we find ourselves needing more bandwidth. 100 Mbps Ethernet promises to deliver the bandwidth we need without the need to rewire or rewrite our existing protocol stacks.
●The transition from 10Base to 100Base Ethernet does present some implementation differences. Given the relatively low data rate of 10Base Ethernet, address filtering in bridge applications was often performed by the host CPU in software. The higher data rate of 100Base Ethernet doesn't allow the host CPU in the bridge enough time to accept orreject frames. There is a need to implement a hardware method to accept or reject frames. This need can be filled by the addition of a Content Addressable Memory to the Ethernet Media Access Controller.
●A bridge would simply present to the CAM a 48–bit MAC address obtained from an incoming frame. The CAMs job is to search its contents and indicate to the MAC if the incoming address was present within the CAM.
●Although CAMs have been available for years, they were often too expensive to justify their use. The MCM69C232 CAM addresses this problem with a different approach to CAM technology. By combining logic with fast and dense SRAM memory cores, Motorola is able to produce cost–ef-fective, fast, and deep CAMs. The MCM69C232 is a 4K x 64 CAM and the MCM69C432 is a 16K x 64 CAM.
●The purpose of this application note is to illustrate the connection of a CAM in a system. The CAM would exist between the Physical Interface Device (the PHY) and the MAC. The AMD79C971 MAC was chosen to illustrate. The MAC has an industry standard interface to the PHY known as a Media Independent Interface. What is needed is a single logic device that can interface the CAM to the MII/PHY connection and signal the MAC to accept or reject an incoming frame. This logic is easily implemented in a FPGA. We will discuss the operation of this FPGA in this application note

Brand of Product：	NXP
Part#：	MCM69C232 More Part#
Product Category：	CAM More
Application：	More
Data Type：	Application note & Design Guide More
Safety & Environment Standards：	More
Operating Temperature：	Please see the document for details
Qualification Grade：	More
Qualification Approval：	More
Package：
Language：	English Chinese Chinese and English Japanese
Date of Creation：	10/3/97
Version Number：
Data Encoding：	AN1726
Data Size：	251 KB

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