Datasheet

Table Of Contents
2. Auto CMD23: when the ACMDEN field is set to 2, the peripheral issues a CMD23 automatically
before issuing a command specified in CR.
The following conditions are required to use Auto CMD23:
A memory card that supports CMD23 (SCR[33] = 1)
If DMA is used, it must be ADMA (SDMA not supported).
Only CMD18 or CMD25 is issued.
Note:  The peripheral does not check the command index.
Auto CMD23 can be used with or without ADMA. By writing CR, the peripheral issues a CMD23 first and
then issues a command specified by the CR.CMDIDX field. If CMD23 response errors are detected, the
second command is not issued. A CMD23 error is indicated in ACESR. The CMD23 argument (32-bit
block count value) is defined in SSAR.
This field determines the use of auto command functions.
Value Name Description
0
DISABLED Auto Command Disabled
1
CMD12 Auto CMD12 Enabled
2
CMD23 Auto CMD23 Enabled
3
Reserved Reserved
Bit 1 – BCEN Block Count Enable
This bit is used to enable BCR, which is only relevant for multiple block transfers. When this bit is 0, BCR
is disabled, which is useful when executing an infinite transfer (refer to Table 1-4). If an ADMA2 transfer is
more than 65535 blocks, this bit is set to 0 and the data transfer length is designated by the Descriptor
Table.
Value Name Description
0
DISABLED Block count is disabled
1
ENABLED Block count is enabled
Bit 0 – DMAEN DMA Enable
This bit enables the DMA functionality described in section “Supporting DMA” in “SD Host Controller
Simplified Specification V3.00” . DMA can be enabled only if it is supported as indicated by the bit
CA0R.ADMA2SUP. One of the DMA modes can be selected using the field HC1R.DMASEL. If DMA is not
supported, this bit is meaningless and then always reads 0. When this bit is set to 1, a DMA operation
begins when the user writes to the upper byte of CR.
Value Name Description
0
DISABLED DMA functionality is disabled
1
ENABLED DMA functionality is enabled
SAM D5x/E5x Family Data Sheet
SD/MMC Host Controller ...
© 2019 Microchip Technology Inc.
Datasheet
DS60001507E-page 1324