GD32F20x User Manual
651
This 2-bit field indicates the T
OFFSET
and one of four values can be selected. This field is
meaningless if ERASE_SIZE and ERASE_TIMEOUT fields are set to 0.
Table 24-30. Erase offset field
ERASE_OFFSET
Value Definition
0h
0 [sec]
1h
1 [sec]
2h
2 [sec]
3h
3 [sec]
24.6.
Programming sequence
24.6.1.
Card identification
After the host is reset, it enters the card identification mode and looks 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
Содержание GD32F20 Series
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Страница 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
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Страница 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
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Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...