SanDisk SDSDB-32-201-80 - Industrial Grade Flash Memory Card Product Manual page 53

Secure Digital (SD) Card Protocol Description
Response tokens have four coding schemes depending on their content. The token length is either 48 or 136 bits.
The CRC protection algorithm for block data is a 16-bit CCITT polynomial. All used CRC types are described in
Section 4.6.
Response content: mirrored command and status
Transmitter bit:
information (R1 response), OCR register (R3 response)
'0'=card response
or RCA (R6) protected by 7 bit CRC checksum
End bt:
Start bit
always '1'
always '0'
0 0 Content 1
R1, R3, R6
End bt:
Total length = 48 bits
always '1'
0 0 Content = CID or CSD CRC 1
R2
Total length = 136 bits
Figure 4-5. Response Token Format
In the CMD line, the MSB bit is transmitted first, whereas the LSB bit is transmitted last.
When the wide bus option is used, the data is transferred 4 bits at a time (see Figure 4-6). Start and end bits, as well
as the CRC bits, are transmitted for every one of the DAT lines. CRC bits are calculated and checked for every
DAT line individually. The CRC status response and Busy indication will be sent by the card to the host on DAT0
only (DAT1-DAT3 during that period are "don't care").
SanDisk Secure Digital (SD) Card Product Manual, Rev. 1.9 © 2003 SANDISK CORPORATION 4-3