MultiMediaCard Protocol - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 95

Table 5-1: MultiMediaCard commands have 48 bits.
Bit(s)

Field Width (bits) Value Description

0 1 End bit Always 1

1..7 7 CRC Error-detect value

8..39 32 Command argument Additional information or

stuff bits (zeros)

40..45 6 Command index Identifies the command

46 1 Transmission bit Always 1 for commands

47 1 Start bit Always zero

Bit 2: An illegal or unsupported command code was received.
Bit 3: CRC error.
Bit 4: An error occurred in the sequence of erase commands.
Bit 5: The device received an address that doesn't match the expected block
length.
Bit 6: The command's argument was out of range.
Bit 7: Always zero.
The RESPONSE_1 union defines a byte or eight bits that can hold an R1
response:
typedef union
{
byte _byte;
struct
{
unsigned IN_IDLE_STATE:1;
unsigned ERASE_RESET:1;
unsigned ILLEGAL_CMD:1;
unsigned CRC_ERR:1;
unsigned ERASE_SEQ_ERR:1;
unsigned ADDRESS_ERR:1;
unsigned PARAM_ERR:1;
unsigned B7:1;
};
} RESPONSE_1;