擴(kuò)展MCU功能時(shí)，明智地使用外部存儲(chǔ)器接口

　　單片機(jī)在許多嵌入式系統(tǒng)設(shè)計(jì)的關(guān)鍵要素，但往往附加功能都需要實(shí)現(xiàn)必要功能。在基于MCU的設(shè)計(jì)中，最受限制的因素之一是片上存儲(chǔ)器。越來(lái)越多的應(yīng)用需要更多的系統(tǒng)內(nèi)存比MCU有。特別是，先進(jìn)的人機(jī)界面（HMI）的設(shè)計(jì)需要一個(gè)顯著量的只讀圖像和音頻信息不容易存儲(chǔ)在MCU片上閃存。此外，越來(lái)越多的應(yīng)用程序發(fā)現(xiàn)片上RAM過(guò)于限制的先進(jìn)通信信道，需要顯著的數(shù)據(jù)緩沖和存儲(chǔ)。

　　本文將回顧一些可用的外部存儲(chǔ)器接口對(duì)現(xiàn)代微控制器。這將幫助設(shè)計(jì)師更有效地實(shí)現(xiàn)基于單片機(jī)的系統(tǒng)需要額外的外部存儲(chǔ)為NVM的閃光或揮發(fā)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.