The function of this bit field is depending on the operation 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 BCR. In this case, 65535 blocks is the
maximum value.