HB288064MM1 Datasheet, PDF (51/79 Pages) Hitachi Semiconductor – MultiMediaCard 64 MByte

HB288064MM1
Bus Transfer Protection
Every MultiMediaCard token transferred on the bus is protected by CRC bits. In SPI mode, the
MultiMediaCard offers a non protected mode which enables systems built with reliable data links to
exclude the hardware or firmware required for implementing the CRC generation and verification
functions. In the non-protected mode the CRC bits of the command, response and data tokens are still
required in the tokens. However, they are defined as “don’t care” for the transmitter and ignored by the
receiver. The SPI interface is initialized in the non protected mode. The host can turn this option on and
off using the CRC_ON_OFF command (CMD59).
Data Read Overview
The SPI mode supports single block read operations only (CMD17 in the MultiMediaCard protocol). Upon
reception of a valid read command the card will respond with a response token followed by a data token of
the length defined in a previous SET_BLOCKLEN (CMD16) command (refer to Figure “Read
Operation”).
Data in
from
host
to card
command
from
card
to host
data from card
Next
to host
commnand
command
Data out
response
data block CRC
Read Operation
A valid data block is suffixed with a 16 bit CRC generated by the standard CCITT polynomial
x¹⁶ + x¹² + x⁵ +1.
The maximum block length is given by READ_BL_LEN, defined in the CSD. If partial blocks are allowed
(i.e. the CSD parameter READ_BL_PARTIAL equals 1), the block length can be any number between 1
and the maximum block size. Otherwise, the only valid block length for data read is given by
READ_BL_LEN. The start address can be any byte address in the valid address range of the card. Every
block, however, must be contained in a single physical card sector. In case of a data retrieval error, the card
will not transmit any data. Instead, a special data error token will be sent to the host. Figure “Read
Operation-Data Error” shows a data read operation which terminated with an error token rather than a data
block.
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