at91sam9260-cj ATMEL Corporation, at91sam9260-cj Datasheet - Page 215

• Manufacturer Part Number: at91sam9260-cj
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

Figure 22-5. Refresh Cycle Followed by a Read Access
22.5.5
22.5.5.1
6221G–ATARM–31-Jan-08
SDRAMC_A[12:0]
D[31:0]
SDWE
(input)
SDCS
SDCK
RAS
CAS
Power Management
Row n
Self-refresh Mode
col c col d
Dnb
Dnc
Three low-power modes are available:
The SDRAM Controller activates one low-power mode as soon as the SDRAM device is not
selected. It is possible to delay the entry in self-refresh and power-down mode after the last
access by programming a timeout value in the Low Power Register.
This mode is selected by programming the LPCB field to 1 in the SDRAMC Low Power Register.
In self-refresh mode, the SDRAM device retains data without external clocking and provides its
own internal clocking, thus performing its own auto-refresh cycles. All the inputs to the SDRAM
device become “don’t care” except SDCKE, which remains low. As soon as the SDRAM device
is selected, the SDRAM Controller provides a sequence of commands and exits self-refresh
mode.
Some low-power SDRAMs (e.g., mobile SDRAM) can refresh only one quarter or a half quarter
or all banks of the SDRAM array. This feature reduces the self-refresh current. To configure this
feature, Temperature Compensated Self Refresh (TCSR), Partial Array Self Refresh (PASR)
and Drive Strength (DS) parameters must be set in the Low Power Register and transmitted to
the low-power SDRAM during initialization.
Dnd
• Self-refresh Mode: The SDRAM executes its own Auto-refresh cycle without control of the
• Power-down Mode: Auto-refresh cycles are controlled by the SDRAM Controller. Between
• Deep Power-down Mode: (Only available with Mobile SDRAM) The SDRAM contents are
SDRAM Controller. Current drained by the SDRAM is very low.
auto-refresh cycles, the SDRAM is in power-down. Current drained in Power-down mode is
higher than in Self-refresh Mode.
lost, but the SDRAM does not drain any current.
t
RP
= 3
t
RC
= 8
Row m
AT91SAM9260
t
RCD
= 3
col a
CAS = 2
Dma
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