UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
288 of 362
NXP Semiconductors
UM10208
Chapter 23: LPC2800 SD/MMC
If the interrupt bit is set in the command register, the timer is disabled and the CPSM waits
for an interrupt request from one of the cards. If the W8PEND bit is set in the command
register, the CPSM enters the PEND state, and waits for a CmdPend signal from the data
path subunit. When CmdPend is detected, the CPSM moves to the SEND state. This
enables the data counter to trigger the stop command transmission.
Note: The CPSM remains in the IDLE state for at least eight MCICLK periods to meet Ncc
and Nrc timing constraints.
shows the MCI command transfer.
4.3.5 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-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 (a CMD1 response), software must ignore the
CRC failed status.
Fig 35. MCI command transfer
MCICLK
State
MCICMD
COMMAND
RESPONSE
COMMAND
IDLE
SEND
WAIT
RECEIVE
IDLE
SEND
HI-Z
controller drives
HI-Z
card drives
HI-Z
controller drives
min 8
MCLK
Table 323. 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.