Datasheet

137
4341H–MP3–10/07
AT8xC51SND2C/MP3B
18.2.3 Command Token Format
As shown in Figure 18-6, commands have a fixed code length of 48 bits. Each command token
is preceded by a Start bit: a low level on MCMD line and succeeded by an End bit: a high level
on MCMD line. The command content is preceded by a Transmission bit: a high level on MCMD
line for a command token (host to card) and succeeded by a 7 - bit CRC so that transmission
errors can be detected and the operation may be repeated.
Command content contains the command index and address information or parameters.
Figure 18-6. Command Token Format
Table 18-1. Command Token Format
18.2.4 Response Token Format
There are five types of response tokens (R1 to R5). As shown in Figure 18-7, responses have a
code length of 48 bits or 136 bits. A response token is preceded by a Start bit: a low level on
MCMD line and succeeded by an End bit: a high level on MCMD line. The command content is
preceded by a Transmission bit: a low level on MCMD line for a response token (card to host)
and succeeded (R1,R2,R4,R5) or not (R3) by a 7 - bit CRC.
Response content contains mirrored command and status information (R1 response), CID regis-
ter or CSD register (R2 response), OCR register (R3 response), or RCA register (R4 and R5
response).
Figure 18-7. Response Token Format
0
Total Length = 48 bits
Content CRC1 1
Bit Position 47 46 45:40 39:8 7:1 0
Width (Bits) 1 1 6 32 7 1
Value ‘0’ ‘1’ - - - ‘1’
Description
Start bit Transmission bit
Command
Index
Argument CRC7 End bit
0
Total Length = 48 bits
Content CRC0 1
R1, R4, R5
0
Total Length = 136 bits
Content = CID or CSD CRC0 1
R2
0
Total Length = 48 bits
Content0 1
R3