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<div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://static.pudn.com/prod/directory_preview_static/62798ee0517cd20ea4d5c39f/bg1.jpg"><div class="c x0 y1 w2 h2"><div class="t m0 x1 h3 y2 ff1 fs0 fc0 sc0 ls0 ws0">深入剖析<span class="_ _0"> </span><span class="ff2 sc1">NAND ash<span class="_ _0"> </span></span>工作原理！</div><div class="t m0 x2 h4 y3 ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">闪存阵列分为一系列<span class="_ _1"> </span></span>128kB<span class="_ _1"> </span><span class="ff1">的区块</span>(block)<span class="ff1">，这些区块是<span class="_ _1"> </span></span>NAND<span class="_ _1"> </span><span class="ff1">器件中最小的可擦除实</span></div><div class="t m0 x2 h4 y4 ff1 fs1 fc1 sc1 ls0 ws0">体。擦除一个区块就是把所有的位<span class="ff3">(bit)</span>设置为<span class="ff3">"1"(</span>而所有字节<span class="ff3">(byte)</span>设置为<span class="_ _1"> </span><span class="ff3">FFh)</span>。有必要通过</div><div class="t m0 x2 h4 y5 ff1 fs1 fc1 sc1 ls0 ws0">编程，将已擦除的位从<span class="ff3">"1"</span>变为<span class="ff3">"0"</span>。最小的编程实体是字节<span class="ff3">(byte)</span>。一些<span class="_ _1"> </span><span class="ff3">NOR<span class="_ _1"> </span></span>闪存能同时执</div><div class="t m0 x2 h4 y6 ff1 fs1 fc1 sc1 ls0 ws0">行读写操作<span class="ff3">(</span>见下图<span class="_ _1"> </span><span class="ff3">1)</span>。虽然<span class="_ _1"> </span><span class="ff3">NAND<span class="_ _1"> </span></span>不能同时执行读写操作，它可以采用称为<span class="ff3">"</span>映射</div><div class="t m0 x2 h4 y7 ff3 fs1 fc1 sc1 ls0 ws0">(shadowing)"<span class="ff1">的方法，在系统级实现这一点。这种方法在个人电脑上已经沿用多年，即将</span></div><div class="t m0 x2 h4 y8 ff3 fs1 fc1 sc1 ls0 ws0">BIOS<span class="_ _1"> </span><span class="ff1">从速率较低的<span class="_ _1"> </span></span>ROM<span class="_ _1"> </span><span class="ff1">加载到速率较高的<span class="_ _1"> </span></span>RAM<span class="_ _1"> </span><span class="ff1">上。 </span></div><div class="t m0 x2 h4 y9 ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">的效率较高，是因为<span class="_ _1"> </span></span>NAND<span class="_ _1"> </span><span class="ff1">串中没有金属触点。</span>NAND<span class="_ _1"> </span><span class="ff1">闪存单元的大小比<span class="_ _1"> </span></span>NOR<span class="_ _1"> </span><span class="ff1">要小</span></div><div class="t m0 x2 h4 ya ff3 fs1 fc1 sc1 ls0 ws0">(4F2<span class="ff1">：</span>10F2)<span class="ff1">的原因，是<span class="_ _1"> </span></span>NOR<span class="_ _1"> </span><span class="ff1">的每一个单元都需要独立的金属触点。</span>NAND<span class="_ _1"> </span><span class="ff1">与硬盘驱动器类</span></div><div class="t m0 x2 h4 yb ff1 fs1 fc1 sc1 ls0 ws0">似，基于扇区<span class="ff3">(</span>页<span class="ff3">)</span>，适合于存储连续的数据，如图片、音频或个人电脑数据。虽然通过把数据</div><div class="t m0 x2 h4 yc ff1 fs1 fc1 sc1 ls0 ws0">映射到<span class="_ _1"> </span><span class="ff3">RAM<span class="_ _1"> </span></span>上，能在系统级实现随机存取，但是，这样做需要额外的<span class="_ _1"> </span><span class="ff3">RAM<span class="_ _1"> </span></span>存储空间。此外，</div><div class="t m0 x2 h4 yd ff1 fs1 fc1 sc1 ls0 ws0">跟硬盘一样，<span class="ff3">NAND<span class="_ _1"> </span></span>器件存在坏的扇区，需要纠错码<span class="ff3">(ECC)</span>来维持数据的完整性。 </div><div class="t m0 x2 h4 ye ff1 fs1 fc1 sc1 ls0 ws0">存储单元面积越小，裸片的面积也就越小。在这种情况下，<span class="ff3">NAND<span class="_ _1"> </span></span>就能够为当今的低成本消费</div><div class="t m0 x2 h4 yf ff1 fs1 fc1 sc1 ls0 ws0">市场提供存储容量更大的闪存产品。<span class="ff3">NAND<span class="_ _1"> </span></span>闪存用于几乎所有可擦除的存储卡。<span class="ff3">NAND<span class="_ _1"> </span></span>的复用</div><div class="t m0 x2 h4 y10 ff1 fs1 fc1 sc1 ls0 ws0">接口为所有最新的器件和密度都提供了一种相似的引脚输出。这种引脚输出使得设计工程师无</div><div class="t m0 x2 h4 y11 ff1 fs1 fc1 sc1 ls0 ws0">须改变电路板的硬件设计，就能从更小的密度移植到更大密度的设计上。</div><div class="t m0 x2 h4 y12 ff2 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1 sc2">与<span class="_ _1"> </span></span>NOR<span class="_ _1"> </span><span class="ff1 sc2">闪存比较<span class="sc1"> </span></span></div><div class="t m0 x2 h4 y13 ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">闪存的优点在于写</span>(<span class="ff1">编程</span>)<span class="ff1">和擦除操作的速率快，而<span class="_ _1"> </span></span>NOR<span class="_ _1"> </span><span class="ff1">的优点是具有随机存取和对字</span></div><div class="t m0 x2 h4 y14 ff1 fs1 fc1 sc1 ls0 ws0">节执行写<span class="ff3">(</span>编程<span class="ff3">)</span>操作的能力<span class="ff3">(</span>见下图图<span class="_ _1"> </span><span class="ff3">2)</span>。<span class="ff3">NOR<span class="_ _1"> </span></span>的随机存取能力支持直接代码执行<span class="ff3">(XiP)</span>，而这</div><div class="t m0 x2 h4 y15 ff1 fs1 fc1 sc1 ls0 ws0">是嵌入式应用经常需要的一个功能。<span class="ff3">NAND<span class="_ _1"> </span></span>的缺点是随机存取的速率慢，<span class="ff3">NOR<span class="_ _1"> </span></span>的缺点是受到</div><div class="t m0 x2 h4 y16 ff1 fs1 fc1 sc1 ls0 ws0">读和擦除速度慢的性能制约。<span class="ff3">NAND<span class="_ _1"> </span></span>较适合于存储文件。如今，越来越多的处理器具备直接</div><div class="t m0 x2 h4 y17 ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">接口，并能直接从<span class="_ _1"> </span></span>NAND(<span class="ff1">没有<span class="_ _1"> </span></span>NOR)<span class="ff1">导入数据。 </span></div><div class="t m0 x2 h4 y18 ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">的真正好处是编程速度快、擦除时间短。</span>NAND<span class="_ _1"> </span><span class="ff1">支持速率超过<span class="_ _1"> </span></span>5Mbps<span class="_ _1"> </span><span class="ff1">的持续写操作，</span></div><div class="t m0 x2 h4 y19 ff1 fs1 fc1 sc1 ls0 ws0">其区块擦除时间短至<span class="_ _1"> </span><span class="ff3">2ms</span>，而<span class="_ _1"> </span><span class="ff3">NOR<span class="_ _1"> </span></span>是<span class="_ _1"> </span><span class="ff3">750ms</span>。显然，<span class="ff3">NAND<span class="_ _1"> </span></span>在某些方面具有绝对优势。然</div><div class="t m0 x2 h4 y1a ff1 fs1 fc1 sc1 ls0 ws0">而，它不太适合于直接随机存取。 </div><div class="t m0 x2 h4 y1b ff1 fs1 fc1 sc1 ls0 ws0">对于<span class="_ _1"> </span><span class="ff3">16<span class="_ _1"> </span></span>位的器件，<span class="ff3">NOR<span class="_ _1"> </span></span>闪存大约需要<span class="_ _1"> </span><span class="ff3">41<span class="_ _1"> </span></span>个<span class="_ _1"> </span><span class="ff3">I/O<span class="_ _1"> </span></span>引脚；相对而言，<span class="ff3">NAND<span class="_ _1"> </span></span>器件仅需<span class="_ _1"> </span><span class="ff3">24<span class="_ _1"> </span></span>个引脚。</div><div class="t m0 x2 h5 y1c ff3 fs1 fc1 sc1 ls0 ws0">NAND<span class="_ _1"> </span><span class="ff1">器件能够复用指<span class="ff4">令</span>、<span class="ff4">地址</span>和数据<span class="ff4">总线</span>，从而节<span class="ff4">省</span>了引脚数量。复用接口的一<span class="ff4">项</span>好处，就</span></div><div class="t m0 x2 h5 y1d ff1 fs1 fc1 sc1 ls0 ws0">在于能够<span class="ff4">利</span>用同样的硬件设计和电路板，支持较大的<span class="_ _1"> </span><span class="ff3">NAND<span class="_ _1"> </span></span>器件。<span class="ff4">由</span>于<span class="ff4">普</span>通的<span class="_ _1"> </span><span class="ff3">TSOP-1<span class="_ _1"> </span><span class="ff4">封装</span></span>已</div><div class="t m0 x2 h5 y1e ff1 fs1 fc1 sc1 ls0 ws0">经沿用多年，<span class="ff4">该</span>功能<span class="ff4">让客户</span>能够把较高密度的<span class="_ _1"> </span><span class="ff3">NAND<span class="_ _1"> </span></span>器件移植到相同的电路板上。<span class="ff3">NAND<span class="_ _1"> </span></span>器件</div><div class="t m0 x2 h5 y1f ff1 fs1 fc1 sc1 ls0 ws0">的<span class="ff4">另</span>外一个好处显然是其<span class="ff4">封装选项</span>：<span class="ff3">NAND<span class="_ _1"> </span></span>提供一种<span class="ff4">厚膜</span>的<span class="_ _1"> </span><span class="ff3">2Gb<span class="_ _1"> </span></span>裸片或能够支持最多<span class="ff4">四颗堆</span></div><div class="t m0 x2 h5 y20 ff4 fs1 fc1 sc1 ls0 ws0">叠<span class="ff1">裸片，容</span>许<span class="ff1">在相同的<span class="_ _1"> </span><span class="ff3">TSOP-1<span class="_ _1"> </span></span></span>封装<span class="ff1">中</span>堆叠<span class="ff1">一个<span class="_ _1"> </span><span class="ff3">8Gb<span class="_ _1"> </span></span>的器件。这就使得一种</span>封装<span class="ff1">和接口能够在</span></div><div class="t m0 x2 h4 y21 ff1 fs1 fc1 sc1 ls0 ws0">将来支持较高的密度。</div></div></div><div class="pi" data-data='{"ctm":[1.611850,0.000000,0.000000,1.611850,0.000000,0.000000]}'></div></div>
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Nand Flash原理
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本资料详细介绍了Nand Flash的工作原理，对于Nand Flash的嵌入式开发很有价值。
NandFlash_Principle.rar
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