MMC/SD Host Controller
7-153
MPU Public Peripherals
Chip-Select Mode (CSM)
When this bit (3) is set to 0 and enabled (CSD=0), the selected CS signal pin
goes active (low) only when SPI transfer is started and brought back automati-
cally to its inactive state (high), when the SPI transfer completes.
When set to 1, the automatic control of the CS signal is disabled. Instead, the
selected CS signal pin is manually controlled by the chip-select disable regis-
ter bit (CSD). This mode provides support for complex SPI transfer scheme
that requires CS to be kept active during the entire transfer (ex: MMC card write
with busy condition).
-
0: Automatic mode
-
1: Manual mode (controlled by CSD)
Value after reset is low.
Chip-Select Disable (CSD)
When this bit (2) is set to 0, the selected CS signal is asserted to its active (low)
state either automatically when CSM = 0, or manually when CSM = 1.
When set to 1, the selected CS signal is forced to its inactive (high) state. It can
be used to send dummy clocks with CS inactive to a MMC or SD card.
-
0: Selected CS is conditionally asserted (low).
-
1: Selected CS is deasserted (high).
Value after reset is low.
Table 7–111. Chip-Select Control (SPI Mode)
CSM
CSD
Selected CS
Comment
0
0
High-low-high
Automatic mode: CS asserted active (low) during SPI
transfer.
0
1
High
Automatic mode: CS forced inactive (high)
1
0
Low
Manual mode: CS asserted active (low)
1
1
High
Manual mode: CS asserted inactive (high)