GD32F20x User Manual
652
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.
If the card cannot operate on the supplied voltage, it returns no response and stays in idle
state. It is mandatory to issue CMD8 prior to ACMD41 to initialize SDHC Card. Receipt of
CMD8 makes the cards realize that the host supports the Physical Layer Version 2.00 and
the card can enable new functions.
Card identification process
The card identification process differs in different cards. The card can be of the type MMC,
CE-ATA, SD, or SD I/O. All types of SD I/O cards are supported, that is, SDIO_IO_ONLY,
SDIO_MEM_ONLY, and SDIO COMBO cards. The identification process sequence includes
the following steps:
Check if the card is connected.
Identify the card type; SD, MMC(CE-ATA), or SD I/O.
–
Send CMD5 first. If a response is received, then the card is SD I/O
–
If not, send ACMD41; if a response is received, then the card is SD.
–
Otherwise, the card is an MMC or CE-ATA.
Initialization the card according to the card type.
Use a clock source with a frequency = F
OD
(that is, 400 KHz) and use the following command
sequence:
–
SD card - Send CMD0, ACMD41, CMD2, CMD3.
–
SDHC card - send CMD0, CMD8, ACMD41, CMD2, CMD3.
–
SD I/O -
Send CMD52, CMD0, CMD5, if the card doesn’t have memory port, send
–
CMD3; otherwise send ACMD41, CMD11 (optional), CMD2, and CMD3.
–
MMC/CE-ATA - Send CMD0, CMD1, CMD2, CMD3.
Identify the MMC/CE-ATA device.
–
CPU should query the byte 504 (S_CMD_SET) of EXT_CSD register by sending
CMD8. If bit 4 is set to 1, then the device supports ATA mode.
–
If ATA mode is supported, the CPU should select the ATA mode by setting the ATA
bit (bit 4) in the EXT_CSD register slice 191(CMD_SET) to activate the ATA
command set. The CPU selects the command set using the SWITCH (CMD6)
command.
Содержание GD32F20 Series
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Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...