Datasheet

T
T
T
r
r
r
a
a
a
n
n
n
s
s
s
c
c
c
e
e
e
n
n
n
d
d
d
I
I
I
n
n
n
d
d
d
u
u
u
s
s
s
t
t
t
r
r
r
i
i
i
a
a
a
l
l
l
C
C
C
F
F
F
C
C
C
a
a
a
r
r
r
d
d
d
T
T
T
S
S
S
1
1
1
2
2
2
8
8
8
M
M
M
~
~
~
1
1
1
6
6
6
G
G
G
C
C
C
F
F
F
2
2
2
0
0
0
0
0
0
I
I
I
Transcend Information Inc.
V1.2
4
More Functions to extend product life
1. Global Wear Leveling – Advanced algorithm to enhance the Wear-Leveling Efficiency
There are 3 main processes in global wear leveling approaches:
(1) Record the block erase count and save in the wear-leveling table.
(2) Find the static-block and save it in wear-leveling pointer.
(3) Check the erase count when the block popped from spare pool. If the
block erase count is bigger
than WEARCNT, then swapped the static-block and over-count-block.
After actual test, global wear leveling successfully even the erase
count of every block; hence, it can
extend the life expectancy of Flash product.
2. StaticDataRefresh Technology – Keeping Data Healthy
There are many variants that would disturb the charge inside a Flash cell. These variants can be:
time,
read operations, undesired charge, heat, etc; each variant would create a charge loss,
and the contents
shift in their charge levels slightly. In our everyday usage –
more than 60% are repeated read operations,
the accumulated charge loss would eventually result in the data loss.
Normally, ECC engine corrections are taken place without affecting the host normal
operations. As
time passes by, the number of error bits accumulated in the read transaction
exceeds the correcting
capability of the ECC engine, resulting in corrupted data being sent to the host.
To prevent this, Transcend’s CF200I monitor the error bit levels at each read
operation; when it
reaches the preset threshold value, the controller automatically performs
data refresh to “restore” the
correct charge levels in the cell. This implementation practically restores the data to its original, error-fr
ee
state, and hence, lengthening the life of the data.
3. EarlyRetirement – Avoiding Data Loss Due to Weak Block
The StaticDataRefresh feature functions well when the cells in a block are still healthy. As
the block
ages over time, it cannot store charge reliably anymore, EarlyRetirement enters the scene.
EarlyRetirement works by moving the static data to another block (a health block) before
the previously
used block becomes completely incapable of holding charges for data. When the charge loss error leve
l
exceeds another threshold value (higher from that for
StaticDataRefresh), the controller automatically
moves its data to another block. In addition,
the original block is then marked as a bad block, which
prevents its further use, and thus the block enters the state of “EarlyRetirement.”
Note that, through this
process, the incorrect data are detected and effectively corrected by
the ECC engine, thus the data in the
new block is stored error-free.