Information Technology Reference
In-Depth Information
Token Formats
Commands that send or request blocks of data use structures called tokens
to hold the data and MultiMediaCard responses. There are three types of
tokens: data, data_response, and data_error.
Data
Data blocks being sent to or from a MultiMediaCard's storage media travel
in data tokens. In SPI mode, each data token consists of a Start Block token
(1 byte) followed by the data block (1 or more bytes) and a CRC value (2
bytes). Table 5-2 shows the values for Start Block tokens and the Stop Tran
token, which a host can send to end a command that is writing multiple
blocks. Note that FEh is the Start Block token for all operations except mul-
tiple block writes.
Data_response
After receiving a data token, the MultiMediaCard returns a 1-byte
data_response token. These are the values of the bits in the data_response
token:
Bit 0: 1.
Bits 3..1: Status
010 = Data accepted
101 = CRC error
110 = Write error
Bit 4: 0.
Bits 5..7: Don't care.
To determines if the data was accepted, firmware can logically AND the
data_response byte with 0Fh. If the result is 05h, the data was accepted.
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