5 command format, Nxp semiconductors – NXP Semiconductors LPC24XX UM10237 User Manual
Page 556
UM10237_4
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 04 — 26 August 2009
556 of 792
NXP Semiconductors
UM10237
Chapter 21: LPC24XX SD/MMC card interface
5.3.5 Command format
The command path operates in a half-duplex mode, so that commands and responses
can either be sent or received. If the CPSM is not in the SEND state, the MCICMD output
is in HI-Z state, as shown in
. Data on MCICMD is synchronous to the rising
MCICLK edge. All commands have a fixed length of 48 bits.
shows the
command format.
The MCI adapter supports two response types. Both use CRC error checking:
•
48 bit short response (see
)
•
136 bit long response (see
Note: If the response does not contain CRC (CMD1 response), the device driver must
ignore the CRC failed status.
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 21–6.4 “Command Register
for more information). The command path implements
Section 21–6.11 “Status Register (MCIStatus
for more information).
Table 482. Command format
Bit Position
Width
Value
Description
0
1
1
End bit.
7:1
7
-
CRC7
39:8
32
-
Argument.
45:40
6
-
Command index.
46
1
1
Transmission bit.
47
1
0
Stat bit.
Table 483. Simple response format
Bit Position
Width
Value
Description
0
1
1
End bit.
7:1
7
-
CRC7 (or 1111111).
39:8
32
-
Argument.
45:40
6
-
Command index.
46
1
0
Transmission bit.
47
1
0
Start bit.
Table 484. Long response format
Bit Position
Width
Value
Description
0
1
1
End bit.
127:1
127
-
CID or CSD (including internal CRC7).
133:128
6
111111
Reserved.
134
1
1
Transmission bit.
135
1
0
Start bit.