擴展MCU功能時，明智地使用外部存儲器接口

　　單片機在許多嵌入式系統設計的關鍵要素，但往往附加功能都需要實現必要功能。在基于MCU的設計中，最受限制的因素之一是片上存儲器。越來越多的應用需要更多的系統內存比MCU有。特別是，先進的人機界面（HMI）的設計需要一個顯著量的只讀圖像和音頻信息不容易存儲在MCU片上閃存。此外，越來越多的應用程序發現片上RAM過于限制的先進通信信道，需要顯著的數據緩沖和存儲。

　　本文將回顧一些可用的外部存儲器接口對現代微控制器。這將幫助設計師更有效地實現基于單片機的系統需要額外的外部存儲為NVM的閃光或揮發性SRAM / DRAM。

　　External memory interfaces to SDRAM

　　Perhaps the most obvious external memory interface needed to extend storage capability is for large working SRAM. Typically， MCUs have a relatively small amount of on-chip SRAM and often an application will require more working memory than is available on-chip. Advanced user interfaces， for example， may require a significant amount of buffer memory for processing graphical user interfaces （GUIs） and creating video or audio prompts. Often， compression techniques are used when these data files are stored or transmitted to reduce local storage requirements or system bandwidth requirements. This means that a significant amount of working storage may be needed to decompress these files. Often， too， large working memories are needed in communications application or in digital-signal processing applications as buffer storage.