Xilinx XAPP169, Примечание к применению

Страница: 8 / 27

8 www.xilinx.com XAPP169 (v1.0) November 24, 1999
1-800-255-7778
MP3 NG: A Next Generation Consumer Platform
R
Samsung
FLASH Memory
The FLASH memory chosen for this design is the KM29U64000T 8M x 8 device from Samsung
Semiconductor. This device is based on NAND FLASH technology and is popular in MP3 player
applications due to its high density and low cost per bit.
Figure 8 shows the block diagram for this device. The complete data sheet for the
KM29U64000T can be found at the following URL:
http://www.usa.samsungsemi.com/products/prodspec/flash/km29u64000(i)t.pdf
Unfortunately this device also has two characteristics that present significant system level
design challenges. The first of these is the narrow, highly multiplexed interface that is used to
access the device. The KM29U64000T interfaces to the system through an 8-bit wide port that
is used for both address and data.
Figure 9 illustrates the read timing for this device.
The second and most challenging issue relates to data integrity, which is an issue common to
most devices using NAND technology. There are two aspects to this, the first of which is the fact
that devices when shipped may have memory blocks that may not be used due to data errors.
The data sheet for the device has a parameter called N
VB
that is the number valid blocks that
the device contains. The value of N
VB
varies from device to device and is specified to have a
minimum of 1014, a maximum of 1024, and typically 1020. While the first block is guaranteed
to be good, bad blocks can occur at any other location within the memory array. Invalid blocks
are marked at the factory by storing a "0" value at location "0" in either the first or second block
of the page. The system level impact of this is that it must keep track of which blocks are good
within the device and that this results in a non-contiguous memory map.
The second issue is that while the device is guaranteed to provide at least the minimum number
of valid blocks over its operational lifetime these devices may experience failures in additional
blocks throughout their life. In order to ensure system integrity some form of error detection and
correction must be implemented.
The discussion of the FLASH memory interface will discuss how these issues were addressed
in this design.
X-Buffers
Y-Gating
64M + 2M Bit
Command
2nd half Page Register & S/A
NAND Flash
ARRAY
(512 + 16)Byte x 16384
Y-Gating
1st half Page Register & S/A
I/O Buffers & Latches
Latches
& Decoders
Y-Buffers
Latches
& Decoders
Register
Control Logic
& High Voltage
Generator
Global Buffers
Output
Driver
A
9
- A
22
A
0
- A
7
Command
CE
RE
WE
CLE ALE WP
I/0 0
I/0 7
V
CC
Q
V
SS
A
8
Figure 8: KM29U64000T Block Diagram
(Courtesy Samsung Semiconductor)