Chapter 4 – SD Card Protocol Description
Revision 2.2 SanDisk SD Card Product Manual
© 2004 SanDisk Corporation 4-3 12/08/04
Each command token is preceded by a start bit (0) and succeeded by an end bit (1). The
total length is 48 bits. CRC bits protect each token to detect transmission errors; the
operation may be repeated.
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
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 four 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 card sends
the host the CRC status response and busy indication on DAT0 only. (DAT1-DAT3 during
that period is “don’t care”).
Figure 4-6 Data Packet Format
"Start" bit
always 0
"End" bit
always 1
Response-content mirrored command and
status information (R1 response). OCR Register
(R3 response) or RCA (R6) protected by 7-bit
CRC checksum
"Transmitter" bit:
1=card response
Total length = 48 bits
0 Content0 1
Total length = 136 bits
0 Content= CID or CSD CRC0 1
"End" bit
always 1
R1, R3, R6
R2
"Start" bit
always 0
"End" bit
always 1
MSB (4095)
Block length
0
Block length /4
"End" bit
always 1
LSB (0)
Standard busy
(only DAT0 used)
CRC 1
DAT3
0 CRC4095 13
DAT2
0 CRC4094 12
DAT1
0 CRC4093 11
DAT0
0 CRC4092 10
MSN
LSN
Wide
bus (all
four data
lines
used)
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