at91sam9263 ATMEL Corporation, at91sam9263 Datasheet - Page 243

• Manufacturer Part Number: at91sam9263
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

22.5.2
Figure 22-3. Read Burst, 32-bit SDRAM Access
6249D–ATARM–20-Dec-07
SDRAM Controller Read Cycle
SDRAMC_A[12:0]
D[31:0]
SDWE
SDCS
(Input)
SDCK
RAS
CAS
The SDRAM Controller allows burst access, incremental burst of unspecified length or single
access. In all cases, the SDRAM Controller keeps track of the active row in each bank, thus
maximizing performance of the SDRAM. If row and bank addresses do not match the previous
row/bank address, then the SDRAM controller automatically generates a precharge command,
activates the new row and starts the read command. To comply with the SDRAM timing param-
eters, additional clock cycles on SDCK are inserted between precharge and active commands
(t
uration register of the SDRAM Controller. After a read command, additional wait states are
generated to comply with the CAS latency (1, 2 or 3 clock delays specified in the configuration
register).
For a single access or an incremented burst of unspecified length, the SDRAM Controller antici-
pates the next access. While the last value of the column is returned by the SDRAM Controller
on the bus, the SDRAM Controller anticipates the read to the next column and thus anticipates
the CAS latency. This reduces the effect of the CAS latency on the internal bus.
For burst access of specified length (4, 8, 16 words), access is not anticipated. This case leads
to the best performance. If the burst is broken (border, busy mode, etc.), the next access is han-
dled as an incrementing burst of unspecified length.
RP
) and between active and read command (t
Row n
t
RCD
= 3
col a
CAS = 2
col b
Dna
col c
AT91SAM9263 Preliminary
Dnb
RCD
col d
). These two parameters are set in the config-
Dnc
col e
Dnd
col f
Dne
Dnf
243