Multimedia Card Registers
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18.5.1.8 SD_BLK Register (offset = 204h) [reset = 0h]
SD_BLK is shown in Figure 18-44 and described in Table 18-27.
This register shall be used for any card. SD_BLK[BLEN] is the block size register. SD_BLK[NBLK] is the
block count register.
Figure 18-44. SD_BLK Register
31 30 29 28 27 26 25 24
NBLK
R/W-0h
23 22 21 20 19 18 17 16
NBLK
R/W-0h
15 14 13 12 11 10 9 8
Reserved BLEN
R-0h R/W-0h
7 6 5 4 3 2 1 0
BLEN
R/W-0h
LEGEND: R/W = Read/Write; R = Read only; W1toCl = Write 1 to clear bit; -n = value after reset
Table 18-27. SD_BLK Register Field Descriptions
Bit Field Type Reset Description
31-16 NBLK R/W 0h Blocks count for current transfer.
This register is enabled when Block count Enable (SD_CMD[1] BCE
bit) is set to 1 and is valid only for multiple block transfers.
Setting the block count to 0 results no data blocks being transferred.
Note: The host controller decrements the block count after each
block transfer and stops when the count reaches zero.
This register can be accessed only if no transaction is executing
(i.e., after a transaction has stopped).
Read operations during transfers may return an invalid value and
write operation will be ignored.
In suspend context, the number of blocks yet to be transferred can
be determined by reading this register.
When restoring transfer context prior to issuing a Resume command,
The local host shall restore the previously saved block count.
0x0 = Stop count
0x1 = 1 block
0x2 = 2 blocks
0xffff = 65535 blocks
15-12 Reserved R 0h
11-0 BLEN R/W 0h Transfer block size.
This register specifies the block size for block data transfers.
Read operations during transfers may return an invalid value, and
write operations are ignored.
When a CMD12 command is issued to stop the transfer, a read of
the BLEN field after transfer completion (SD_STAT[1] TC bit set to
1) will not return the true byte number of data length while the stop
occurs but the value written in this register before transfer is
launched.
0x0 = No data transfer
0x1 = 1 byte block length
0x2 = 2 bytes block length
0x3 = 3 bytes block length
0x1ff = 511 bytes block length
0x200 = 512 bytes block length
0x7ff = 2047 bytes block length
0x800 = 2048 bytes block length
3404
Multimedia Card (MMC) SPRUH73H–October 2011–Revised April 2013
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