GD32F20x User Manual
718
Activate
The activate command activates an idle bank. It presents a 2-bit bank address
EXMC_A[15:14] and a 13-bit row address EXMC_A[12:0], and causes a read of that row into
the b
ank’s array of 16,384 column sense amplifiers. This also known as opening the row. This
operation has the side effect of refreshing the dynamic memory storage cells of that row.
Once the row has been activated, read/write commands are possible to that row. Activation
requires a minimum amount of time, called the row-to-column delay (RCD) before read/write
to it may occur. This time, rounded up to the next multiple of the clock period, specifies the
minimum number of wait cycles between an active command and a read/write command.
During these wait cycles, additional commands may be sent to other banks, because each
bank operates completely independently.
Read/Write access
SDRAMC can translate AHB single and burst read operation into single memory access.
SDRAMC always keeps track of the activated row number in order to perform consecutive
read access. If the next read location is in the same row or another active row, read access
is proceeded without interruption, else a precharge command is issued to deactivate the
current row, followed by the activation of the row where the next read access is targeted, and
then the read access is performed. A read FIFO is design to cache the read data during CAS
latency and pipe line delay (PIPED), Burst read (BRSTRD) must be set in order to enable the
FIFO.
The following diagram shows a burst read access to an in active row, a row activation
command is issued before read access. If read operation were performed on an active row,
row address strobe is not necessary, only column address strobe is needed.
Figure 25-30. Burst read operation
Chip Enable
(EXMC_SDNEx)
Column Address
Strobe
(EXMC_NCAS)
Row Address
Strobe
(EXMC_NRAS)
Write Enable
(EXMC_SDNWE)
Data
(EXMC_D[31:0])
Clock
(EXMC_SDCLK)
Address
(EXMC_A[12:0])
Col
m
Col
m+1
bank
a
Col
m+3
Col
m+4
Col
m+2
RCD = 3
Active Row
Read
Command
Row
n
Bank Address
(EXMC_A[15:14])
Col
m+5
Col
m+6
Col
m+7
bank
a
Col
m
Col
m+1
Col
m+3
Col
m+4
Col
m+2
Col
m+5
Col
m+6
Col
m+7
CL = 3
An internal generated clock, which has an adjustable delay from the HCLK can be used to
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