Campbell Scientific CR9000X Measurement and Control System - Manual (Page 415)

Appendix C. PC/CF Card Information
PC or CompactFlash (CF) cards provide a relatively inexpensive, off-the-shelf
means of retrieving data from many of our CRBasic dataloggers or expanding
the on-board datalogger memory. The datalogger’s memory can be expanded
up to 2 Gbytes with the use of these cards. The CR9000X requires a Compact
Flash adapter (CF1) to use compact flash cards. It can directly accommodate
Type 1, Type 2, and Type 3 flash memory cards.
PC/CF cards use NAND (Not AND) Flash (non-volatile) memory which has
the following characteristics: high density, low cost/bit, sequential access,
scalable, and a single standard. There are two types of NAND Flash memory:
Single-Level Cell (SLC) and Multi-Level Cell (MLC). SLC NAND Flash
sometimes called Binary Flash, store one bit of data per memory cell and has
two states: erased (1) or programmed (0). MLC NAND Flash store two bits of
data per memory cell and has four states: erased (11), two thirds (10), one
third (01), or programmed (00)
1 . At first glance, the MLC cards seem more
desirable, because each cell can hold more information. However, as
summarized in Table C-2, the increased data storage comes at a price, mainly
speed.
TABLE C-2. SLC and MLC Performance Characteristics
SLC MLC
Voltage 3.3 V / 1.8 V 3.3 V
Page Size / Block Size 2KB / 128KB 512 B / 32 KB or 2 KB /
256 KB
Access Time (maximum) 25 µs 70 µs
Page Program Time 250 µs 1.2 ms
Partial Programming Yes No
Endurance 100,000 10,000
Write Data Rate 8 MB/s+ 1.5 MB/s
There is a notable performance difference between the two types of NAND
Flash memory. In a performance study by Samsung Electronics
2 , Samsung
found that SLC outperformed MLC, offering greater durability, running 300%
faster in write mode, and 43% faster in read mode. While MLC Flash
increases the overall density of data storage, which therefore decreases cost; it
does so at the expense of data reliability, performance and memory
management. Furthermore, MLC technology is more prone to failure, data
corruption, or incorrect reading due to memory cell degradation from the
additional energy required during operations
2 .
There are two types of CF cards available today: Industrial grade and Standard
or Commercial grade. Industrial grade PC/CF cards are held to a higher
standard; specifically they operate over a wider temperature range, offer better
vibration and shock resistance, and have faster read/write times than their
commercial counterparts (Table C-3). The Industrial Grade cards more closely
match the operating envelope of the dataloggers, and for this reason we
C-1