Espressif ESP32 Technical Reference Manual page 214

9 SD/MMC Host Controller
Continued from the previous page...
UPDATE_CLOCK_REGISTERS_ONLY (R/W)
0: Normal command sequence.
1: Do not send commands, just update clock register value into card clock domain
Following register values are transferred into card clock domain: CLKDIV, CLRSRC, and CLKENA.
Changes card clocks (change frequency, truncate off or on, and set low-frequency mode). This
is provided in order to change clock frequency or stop clock without having to send command
to cards.
During normal command sequence, when update_clock_registers_only = 0, following control
registers are transferred from BIU to CIU: CMD, CMDARG, TMOUT, CTYPE, BLKSIZ, and BYTCNT.
CIU uses new register values for new command sequence to card(s). When bit is set, there are
no Command Done interrupts because no command is sent to SD_MMC_CEATA cards.
CARD_NUMBER Card number in use. Represents physical slot number of card being accessed. In
MMC-Ver3.3-only mode, up to two cards are supported. In SD-only mode, up to two cards are
supported. (R/W)
SEND_INITIALIZATION (R/W)
0: Do not send initialization sequence (80 clocks of 1) before sending this command.
1: Send initialization sequence before sending this command.
After power on, 80 clocks must be sent to card for initialization before sending any commands
to card. Bit should be set while sending first command to card so that controller will initialize
clocks before sending command to card.
STOP_ABORT_CMD (R/W)
0: Neither stop nor abort command can stop current data transfer. If abort is sent to function-
number currently selected or not in data-transfer mode, then bit should be set to 0.
1: Stop or abort command intended to stop current data transfer in progress. When open-ended
or predefined data transfer is in progress, and host issues stop or abort command to stop data
transfer, bit should be set so that command/data state-machines of CIU can return correctly to
idle state.
WAIT_PRVDATA_COMPLETE (R/W)
0: Send command at once, even if previous data transfer has not completed;
1: Wait for previous data transfer to complete before sending Command.
The wait_prvdata_complete = 0 option is typically used to query status of card during data trans-
fer or to stop current data transfer. card_number should be same as in previous command.
SEND_AUTO_STOP (R/W)
0: No stop command is sent at the end of data transfer;
1: Send stop command at the end of data transfer.
Continued on the next page...
Espressif Systems
Register 9.11. CMD_REG (0x002C)
214
Submit Documentation Feedback
ESP32 TRM (Version 5.2)