Atmel SAM9X25, Manual

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SAM9X25
Figure 30-15. Burst Read Access, Latency = 3, DDR2-SDRAM Devices
Figure 30-16. Burst Read Access, Latency = 2, SDR-SDRAM Devices
30.5.3 Refresh (Auto-refresh Command)
An auto-refresh command is used to refresh the DDRSDRC. Refresh addresses are generated
internally by the SDRAM device and incremented after each auto-refresh automatically. The
DDRSDRC generates these auto-refresh commands periodically. A timer is loaded with the
value in the register DDRSDRC_TR that indicates the number of clock cycles between refresh
cycles. When the DDRSDRC initiates a refresh of an SDRAM device, internal memory accesses
are not delayed. However, if the CPU tries to access the SDRAM device, the slave indicates that
the device is busy. A request of refresh does not interrupt a burst transfer in progress.
Col a
NOP READ NOP
0
Latency = 3
SDCLK
A[12:0]
COMMAND
BA[1:0]
DQS[1:0]
Da Db
Dc
Dd De Df Dg Dh
D[15:0]
3 DM[1:0]
Latency = 2
SDCLK
col a A[12:0]
NOP READ NOP BST NOP COMMAND
0
BA[1:0]
DaDb DcDd DeDf Dg Dh D[31:0]
F
DM[3:0]
DQS[1:0]