This Application Note
explains how the Bad Block Management module of the Hardware Adaptation
Layer
(HAL) software, is used to recognize factory generated Bad Blocks
and to manage Bad Blocks that develop during the lifetime of the
NAND Flash device.
INTRODUCTION
Bad Blocks are blocks that contain one or more invalid bits whose
reliability is not guaranteed. Bad Blocks may be present when
the device is shipped, or may develop during the lifetime of the
device.
Devices with Bad Blocks have the same quality level and the
same AC and DC characteristics as devices
where all the blocks are valid. A Bad Block does not affect the
performance of valid blocks because it is isolated from the bit
line and common source line by a select transistor.
Bad Block Management, Block Replacement and the Error Correction
Code software are necessary to
manage the error bits in NAND Flash devices. ST provides this
software in modules in the Hardware Adaptation Layer (HAL) which
manages the hardware functions of the NAND Flash (see Figure 1.
and refer to Application notes AN1820, AN1823).
Refer to Table 1. for the full list of NAND Flash memories covered
by the HAL software and for further information refer to the NAND128-A,
NAND256-A, NAND512-A, NAND01G-A, 528 Byte/ 264 Word Page
datasheet. |