MultiMediaCardTM
2.6.5 Memory Array Partitioning
Although the MultiMediaCard memory space is byte addressable with addresses ranging from 0 to the
last byte, it is not a simple byte array but divided into several structures. Memory bytes are grouped
into 512 byte blocks called sectors. Every block can be read, written individually.
Erase group is a number of sectors. Its size is the number of consecutive sectors. Any combination of
erase groups can be erased in a single erase command. A write command implicitly erases the
memory before writing new data into it. Explicit erase command can be used for pre-erasing of memory
to speed up the next write operation.
Write Protect Groups (WPG) is the minimal units that may have individual write protection. Its size is
the number of erase units that will be write protected by on bit. The write/erase access to each WPG
can be limited individually. The number of various memory structures, for the different MultiMediaCards
are summarized in Table 2-1
Table 2-1 Memory Array Structure
Bytes
32MB
62,720
1,960
64MB
125,440
3,920
128MB
250,880
980
256MB
501,760
1,960
512MB
1,003,520
3,920
1GB
2,007,040
7,840
Sectors
Erase
Group
WPG
490
980
245
490
980
1,960
Read and Write Operations
The MultiMediaCard supports two read/write modes.
Single Block Mode
In this mode the host reads or writes one data block in a pre-specified length block transmission is
protected with 16 bit CRC which is generated by the sending unit and checked by the receiving unit.
Misalignment is not allowed. Every data block must be contained in a single memory sector. The block
length for write operations must be identical to the sector size and the start address aligned to a sector
boundary.
Multiple Block Mode
This mode is similar to the single block mode, but the host can read/write multiple data blocks (all have
the same length) which will be stored or retrieved from contiguous memory addresses starting at the
address specified in the command.
The operation is terminated with a stop transmission command. Misalignment and block length
restrictions apply to multiple blocks as well and are identical to the single block read/write operations.
Multiple block read with pre-defined block is supported.
2.6.6 Data Transfer Rate
The average data transfer rate for the MultiMediaCard is 1 Mbyte/sec for read and 300 Kbyte/Sec for
write (erase time is included) at 3.3 Volts. In block mode, where time gaps can be inserted between
data blocks, the maximum clock frequency is 20MHz. The typical access time (latency) for each data
block, in read operation, is 1.5ms. The write block operation is done in handshake mode. The card will
keep data line DAT low as long as the write operation is in progress and there are no write buffers
available
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