GD32F10x User Manual
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19.6.
Programming sequence
19.6.1.
Card identification
The host will be in card identification mode after reset and while it is looking for new cards on
the bus. While in card identification mode the host resets all the cards, validates operation
voltage range, identifies cards and asks them to publish Relative Card Address (RCA). This
operation is done to each card separately on its own CMD line. All data communication in the
Card Identification Mode uses the command line (CMD) only.
During the card identification process, the card shall operate in the clock frequency of the
identification clock rate F
OD
(400 kHz).
Card reset
The command GO_IDLE_STATE (CMD0) is the software reset command and sets MMC and
SD memory card into Idle State regardless of the current card state. The reset command
(CMD0) is only used for memory or the memory portion of Combo cards. In order to reset an
I/O only card or the I/O portion of a combo card, use CMD52 to write 1 to the RES bit in the
CCCR. Cards in Inactive State are not affected by this command.
After power-on by the host, all cards are in Idle State, including the cards that have been in
Inactive State before. After power-on or CMD0, all cards' CMD lines are in input mode, waiting
for start bit of the next command. The cards are initialized with a default relative card address
(RCA) and with a default driver strength with 400 KHz clock frequency.
Operating voltage range validation
At the start of communication between the host and the card, the host may not know the card
supported voltage and the card may not know whether it supports the current supplied voltage.
To verify the voltage, the following commands are defined in the related specification.
The SEND_OP_COND (CMD1 for MMC), SD_SEND_OP_COND (ACMD41 for SD memory),
IO_SEND_OP_COND (CMD5 for SD I/O) command is designed to provide hosts with a
mechanism to identify and reject cards which do not match the V
DD
range desired by the host.
This is accomplished by the host sending the required V
DD
voltage window as the operand of
this command. If the card cannot perform data transfer in the specified range, it must discard
itself from further bus operations and go into Inactive State. Otherwise, the card shall respond
sending back its V
DD
range.
If the card can operate on the supplied voltage, the response echoes back the supply voltage
and the check pattern that were set in the command argument.
Содержание GD32F10 Series
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