The function of this bit field depends on the operational mode:
For a SDMA transfer, this field is the system memory address. When
the peripheral stops an SDMA transfer, this field points to the system address
of the next contiguous data position. This field 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. An interrupt can be
generated to instruct the software to update this field. Writing the next system
address of the next data position restarts the SDMA transfer.
When executing Auto CMD23, this field is used with Auto
CMD23 to set a 32-bit block count value to the CMD23 argument. If Auto CMD23 is
used with ADMA, the full 32-bit block count value can be used. If Auto CMD23 is
used without ADMA, the available block count value is limited by SDHC_BCR. In
this case, 65535 blocks is the maximum value.