If bit inverse happens in the important file, it will cause a system shut-down. New bad blocks can be generated during usage so the system will have to identify these blocks.īit inverse is easier to find in NAND flash. Erasing and programming factory-marked bad block are prohibited.īad blocks have been initialized before shipping and marked in the specific area. Invalid blocks are defined as blocks that contain one or more bad bits. Additional invalid blocks may develop while being used. The NAND flash may include invalid blocks when they are first shipped.
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Also, like a hard disk, NAND devices have bad blocks, and require error-correcting code (ECC) to maintain data integrity. Although random access can be accomplished at the system level by shadowing the data to RAM, doing so requires additional RAM storage.
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It's sector-based or page-based and suited for storing sequential data such as pictures, audio, or PC data. However, more processors include a direct NAND interface and can boot directly from NAND (without NOR). NAND is better suited for file applications. The disadvantages for NAND are slow random access, while NOR is hampered by are slow write and erase performance. NOR's random access ability allows for execute in place capability, which is often a requirement in embedded applications. In addition, NAND's advantages are fast write (program) and erase operations while NOR's advantages are random access and byte write capability. NAND flash devices hold the advantages of large capacity with low cost compared to NOR FLASH devices. Each page has 2112 bytes total, comprised of a 2048-byte data area and a 64-byte spare area. For a 2-Gbit NAND device, it is organized as 2048 blocks, with 64 pages per block (Figure 1). A block consists of many pages, but because the “Spare area" is reserved for bad block mark and ECC values, only the “Main area" is available to the user. Before reading this article the user should know certain keywords such asīlock, ECC, main area and spare area which are used in NAND datasheets.įor most NAND flash chips, there are 512x8 (or 256x16) or 2048x8 (or 1024x16) bits in the “Main area," and 16x8 (or 8x16) or 64*8 (or 32x16) bits in the “Spare area" for a total of 528x8 (264x16) or 2112x8 (or 1056x16) bits per page.
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This article describes how to program NAND Flash devices using a Xeltek universal programmer.
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