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AT32F435/437
Series Reference Manual
2022.11.11
Page 530
Rev 2.03
After the initialization, the SDRAM is ready to accept commands. If a system reset occurs during an on-
going SDRAM access, the SDRAM device has to be reset after re-initialization in order to issue a new
access to the SDRAM.
If the “Load Mode Register” and “Self-Refresh” commands are applied to both devices at the same time,
access commands are issued using the timing parameters configured for SDRAM device 1.
SDRAM controller write operation
Before performing any write access, the SDRAM write protection must be disabled by clearing the WRP
bit in the SDRAM_CTRLx register, otherwise, an AHB error may occur.
The SDRAM controller translates single or burst AHB write requests into a single SDRAM write access,
which can be done by setting BL=1. In both cases, the SDRAM controller always tries to translate
consecutive or discontinuous AHB write requests into a single SDRAM write request in order to increase
efficiency.
The SDRAM controller keeps track of the active row for each BANK in order to be able to perform
consecutive write accesses to different banks (multibank ping-pong access). If the next write access is
in the same row or in another active row, the write operation is performed. If the next write access targets
an inactive row, the SDRAM controller generates a precharge command (The BANK where the inactive
row is has other open rows, if no other rows, the precharge is unnecessary), and activates the new row
and initiates a write operation.
Figure 24-22
SDRAM write access waveforms (Trcd=2, 9 consecutive write access)
XMC_
SDCS
XMC_
A[12:0]
XMC_
SDNRAS
XMC_
SDNCAS
XMC_
SDNWE
XMC_
D[15:0]
Row 1
Col1 Col2 Col3 Col4 Col5 Col6 Co7 Col8 Col9
DQ1 DQ2 DQ3 DQ4 DQ5 DQ6 DQ7 DQ8 DQ9
XMC_
SDCLK
XMC_
A[15:14]
2'b00
SDRAM controller read operation
The SDRAM controller translates single or burst AHB read requests into a single SDRAM read access,
which can be done by setting BL=1.
The SDRAM controller keeps track of the active row for each BANK in order to be able to perform
consecutive read accesses to different banks (multibank ping-pong access). If the next read access is
in the same row or in another active row, the read operation is performed. If the next read access targets
an inactive row, the SDRAM controller generates a precharge command (The BANK where the inactive
row is has other open rows, if no other rows, the precharge is unnecessary), and activates the new row
and initiates a read operation.
Note: The above-mentioned description applies to the scenario where the SDRAM consecutive read
feature is not enabled (that is, read FIFO is unused.)