UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 556 o f 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 Figure 21–108. Data on MCICMD is synchronous to the rising
MCICLK edge. All commands have a fixed length of 48 bits. Table21–482 shows the
command format.
The MCI adapter supports two response types. Both use CRC error checking:
48 bit short response (see Table21–483)
136 bit long response (see Table21–484)
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
(MCICommand - 0xE008 C00C) for more information). The command path implements
the status flags shown in Table21–485 (see Section 21–6.11 “Status Register (MCIStatus
- 0xE008 C034) for more information).
Table 482. Co mman d 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. Sim ple response format
Bit Position Width Value Description
0 1 1 End bit.
7:1 7 - C RC7 ( or 1111111) .
39:8 32 - Argument.
45:40 6 - Command index.
46 1 0 Transmission bit.
47 1 0 Start bit.
Table 484. Long resp onse format
Bit Position Width Value Description
0 1 1 End bit.
127:1 127 - CID or CSD (including internal CRC7).
133 :128 6 111111 Res erve d.
134 1 1 Transmission bit.
135 1 0 Start bit.