Multimedia Card Registers
18.5.1.15 SD_DATA Register (offset = 220h) [reset = 0h]
SD_DATA is shown in
and described in
.
This register is the 32-bit entry point of the buffer for read or write data transfers. The buffer size is
32bitsx256(1024 bytes). Bytes within a word are stored and read in little endian format. This buffer can be
used as two 512 byte buffers to transfer data efficiently without reducing the throughput. Sequential and
contiguous access is necessary to increment the pointer correctly. Random or skipped access is not
allowed. In little endian, if the local host accesses this register byte-wise or 16bit-wise, the least significant
byte (bits [7:0]) must always be written/read first. The update of the buffer address is done on the most
significant byte write for full 32-bit DATA register or on the most significant byte of the last word of block
transfer. Example 1Byte or 16-bit access: Mbyteen[3:0]=0001 (1-byte) => Mbyteen[3:0]=0010 (1-byte) =>
Mbyteen[3:0]=1100 (2-bytes) OK. Mbyteen[3:0]=0001 (1-byte) => Mbyteen[3:0]=0010 (1-byte) =>
Mbyteen[3:0]=0100 (1-byte) OK. Mbyteen[3:0]=0001 (1-byte) => Mbyteen[3:0]=0010 (1-byte) =>
Mbyteen[3:0]=1000 (1-byte) Bad.
Figure 18-51. SD_DATA Register
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
DATA
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; W1toCl = Write 1 to clear bit; -n = value after reset
Table 18-34. SD_DATA Register Field Descriptions
Bit
Field
Type
Reset
Description
31-0
DATA
R/W
0h
Data register
[31:0].
In functional mode (SD_CON[4] MODE bit set to the default value 0):
A read access to this register is allowed only when the buffer read
enable status is set to 1 (SD_PSTATE[11] BRE bit), otherwise a bad
access (SD_STAT[29] BADA bit) is signaled.
A write access to this register is allowed only when the buffer write
enable status is set to 1 (SD_PSTATE[10] BWE bit), otherwise a bad
access (SD_STAT[29] BADA bit) is signaled and the data is not
written.
3415
SPRUH73H – October 2011 – Revised April 2013
Multimedia Card (MMC)
Copyright © 2011–2013, Texas Instruments Incorporated