ST STM32L4x6 User Manual

SD/SDIO/MMC card host interface (SDMMC) RM0351
1402/1693 DocID024597 Rev 3
The command register contains the command index (six bits sent to a card) and the
command type. These determine whether the command requires a response, and whether
the response is 48 or 136 bits long (see Section 41.8.4 on page 1437). The command path
implements the status flags shown in Table 223:
The CRC generator calculates the CRC checksum for all bits before the CRC code. This
includes the start bit, transmitter bit, command index, and command argument (or card
status). The CRC checksum is calculated for the first 120 bits of CID or CSD for the long
response format. Note that the start bit, transmitter bit and the six reserved bits are not used
in the CRC calculation.
The CRC checksum is a 7-bit value:
CRC[6:0] = Remainder [(M(x) * x
7
) / G(x)]
G(x) = x
7
+ x
3
+ 1
M(x) = (start bit) * x
39
+ ... + (last bit before CRC) * x
0
, or
M(x) = (start bit) * x
119
+ ... + (last bit before CRC) * x
0
Table 221. Short response format
Bit position Width Value Description
47 1 0 Start bit
46 1 0 Transmission bit
[45:40] 6 - Command index
[39:8] 32 - Argument
[7:1] 7 - CRC7(or 1111111)
011End bit
Table 222. Long response format
Bit position Width Value Description
135 1 0 Start bit
134 1 0 Transmission bit
[133:128] 6 111111 Reserved
[127:1] 127 - CID or CSD (including internal CRC7)
0 1 1 End bit
Table 223. Command path status flags
Flag Description
CMDREND Set if response CRC is OK.
CCRCFAIL Set if response CRC fails.
CMDSENT Set when command (that does not require response) is sent
CTIMEOUT Response timeout.
CMDACT Command transfer in progress.

ST STM32L4x6 Specifications

General

Brand	ST
Model	STM32L4x6
Category	Microcontrollers
Language	English