ST STM32F101xx User Manual

Secure digital input/output interface (SDIO) RM0008
552/1096 Doc ID 13902 Rev 12
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 22.9.4 on page 586). The command path
implements the status flags shown in Tabl e 1 40 :
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 138. 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 139. 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 11End bit
Table 140. 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 STM32F101xx Specifications

General

Brand	ST
Model	STM32F101xx
Category	Microcontrollers
Language	English