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GD32F20x User Manual
657
max read frequence = min
(
TRAN_SPEED,
8*2
READ_BL_LEN
-100*NSAC
TAAC*R2W_FACTOR
)
(24-3)
TRAN_SPEED
: Max bus clock frequency.
READ_BL_LEN
: Max read data block length.
NSAC
: Data read access-time 2 in CLK cycles.
TAAC
: Data read access-time 1.
R2W_FACTOR
: Write speed factor.
All the parameters are defined in CSD register. If the host attempts to use a higher frequency,
the card may not be able to process the data and will stop programming, and while ignoring
all further data transfer, wait (in the Receive-data-State) for a stop command. As the host
sends CMD12, the card will respond with the RXORE bit set and return to Transfer state
24.6.6.
Erase
The erasable unit of the MMC/SD memory is the “Erase Group”; Erase group is measured in
write blocks which are the basic writable units of the card. The size of the Erase Group is a
card specific parameter and defined in the CSD.
The host can erase a contiguous range of Erase Groups. Starting the erase process is a three
steps sequence. First the host defines the start address of the range using the
ERASE_GROUP_START (CMD35)/ERASE_WR_BLK_START (CMD32) command, next it
defines
the
last
address
of
the
range
using
the
ERASE_GROUP_END
(CMD36)/ERASE_WR_BLK_END(CMD33) command and finally it starts the erase process
by issuing the ERASE (CMD38) command. The address field in the erase commands is an
Erase Group address in byte units. The card will ignore all LSB’s below the Erase Group size,
effectively rounding the address down to the Erase Group boundary.
If an erase command (CMD35, CMD36, and CMD38) is received out of the defined erase
sequence, the card shall set the ERASE_SEQ_ERROR bit in the status register and reset
the whole sequence.
If the host provides an out of range address as an argument to CMD35 or CMD36, the card
will reject the command, respond with the ADDRESS_OUT_OF_RANGE bit set and reset the
whole erase sequence.
If an ‘non erase’ command (neither of CMD35, CMD36, CMD38 or CMD13) is received, the
card shall respond with the ERASE_RESET bit set, reset the erase sequence and execute
the last command.
If the erase range includes write protected blocks, they shall be left intact and only the non-
protected blocks shall be erased. The WP_ERASE_SKIP status bit in the status register shall
be set.
As described above for block write, the card will indicate that an erase is in progress by
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...