MultiMediaCard Protocol - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 102

Table 5-5: Block read and write commands used by mass-storage devices.
Index

Abbreviation Argument Response Description

CMD12 STOP_TRANSMISSION 00000000h R1 Stop multiple

block read.

CMD15 SET_BLOCK_LEN Block length R1 Set the block

size in bytes for
block read and
block write.

CMD17 READ_SINGLE_BLOCK Starting address

to read

R1 Read a block of

data.

CMD18 READ_MULTIPLE_BLOCK Starting address

to read

R1 Read multiple

blocks of data.

CMD23 SET_BLOCK_COUNT 31..16: 0000h;

15..0: number of
blocks

R1 Set the number

of blocks to
transfer in a
multiple-block
read or write
command.

CMD24 WRITE_SINGLE_BLOCK Starting address

to write to

R1 Write a block of

data.

CMD25 WRITE_MULTIPLE_BLOCK Starting address

to write to

R1 Write multiple

blocks of data.

each command, the host sends a command block and the device sends a
response. For some commands, the device follows the response with one or
more data tokens. For other commands, the host follows the response with
one or more data tokens, and the device sends a response after receiving each
data token.

Timing Considerations

Communications on the SPI bus must meet the timing and clocking
requirements in the MultiMediaCard specification. The host must generate
clock cycles when sending a command or data, when receiving a response or
data token from a card, and when waiting for a response or data token from
a card. The host also must generate 8 clock cycles after all of a command's
communications are complete.
When generating clock cycles and not transmitting a command or data, the
host must hold DataIn high. A PIC18F4550 host can send eight clock