Datasheet

Figure 6-1: Write Protection Hierarchy
For block oriented commands, the following definition is used:
• Block: is the un
it that is related to the block oriented read and write commands. Its size is the number of bytes that will be transferred when one block
command is sent by the host. The size of a block is either pr
ogrammable or fixed. The information about allowed block sizes and the programmability
is stored in the CSD.
• For
devices that have erasable memory cells, special erase commands are defined. The granularity of the erasable units is in general not the same as
for the block oriented commands:
• Sector:
is the unit that is related to the erase commands. Its size is the number of blocks that will be erased in one portion. The size of a sector is fixed
for each device. The information about the sector size (in blocks)
is stored in the CSD. Note that if the card specifies AU size, sector size should
be ignored.
• AU (Allo
cation Unit): is a physical boundary of the card and consists of one or more blocks and its size depends on each card. The maximum AU size
is defined for memory capacity. Furthermore AU is the minimal unit in which the
card guarantees its performance for devices which complies with Speed
Class Specification. The information about the size and the Spee
d Class are stored in the SD Status. AU is also used to calculate the erase timeout.
• WP-
Group: is the minimal unit that may have individual write protection for devices which support write-protected group. Its size is the number of groups
that will be write-protected by one bit. The size of a WP-gr
oup is fixed for each device. The information about the size is stored in the CSD.
The High Capacity SD Memory Card does not support the write protect group command.
- 30 -
datasheet SD Card
Rev. 1.0
MMBTFxxGWBCA-xMExx
6.6 Memory Array Partitioning
The basic unit of data transfer to/from the SD Card is one byte. All data transfer operations which require a block size always define block lengths as inte-
ger multiples of bytes. Some special functions need other partition granularity.
WP Group K
WP Group 2
Sector m
Sector 3
Sector 1
Block 1 Block 2 Block 3 Block n
WP Group 1
SD Memory Card
Sector 2