NAND128W3A0CN1中文资料(20)

NAND128-A, NAND256-A, NAND512-A, NAND01G-A

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DEVICE OPERATIONS

Pointer Operations

As the NAND Flash memories contain two differ-ent areas for x16 devices and three different areas for x8 devices (see Figure 11.) the read command codes (00h, 01h, 50h) are used to act as pointers to the different areas of the memory array (they se-lect the most significant column address).

The Read A and Read B commands act as point-ers to the main memory area. Their use depends on the bus width of the device.■In x16 devices the Read A command (00h)

sets the pointer to Area A (the whole of the main area) that is Words 0 to 255.■In x8 devices the Read A command (00h) sets

the pointer to Area A (the first half of the main area) that is Bytes 0 to 255, and the Read B command (01h) sets the pointer to Area B (the second half of the main area) that is Bytes 256 to 511.

In both the x8 and x16 devices the Read C com-mand (50h), acts as a pointer to Area C (the spare memory area) that is Bytes 512 to 527 or Words 256 to 263.

Once the Read A and Read C commands have been issued the pointer remains in the respective areas until another pointer code is issued. Howev-er, the Read B command is effective for only one operation, once an operation has been executed in Area B the pointer returns automatically to Area A.

The pointer operations can also be used before a program operation, that is the appropriate code (00h, 01h or 50h) can be issued before the pro-gram command 80h is issued (see Figure 12.).

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