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SDRAM Controller (SDRC) Subsystem
10.2.5.4.3.2 Clock-Controlled Memory Power Management
The SDRC power-management register (SDRC.
) contains the EXTCLKDIS field,
which controls suspension of the external clock on a per-CS basis. Writing 1 to this field in the relevant
register freezes the clock with a latency dependent on the SDRC.
register
programming. Subsequently, writing 0 to this field in the relevant register enables the clock with a latency
dependent on the SDRC.
register programming.
10.2.5.4.3.3 Manual Power-Down Mode Power Management
For dynamic power-down mode refer to
, Power-Saving Features. The programming
model for manual power-down mode is different for an SDR and a DDR.
SDR Mechanism/Power-Down Mode Entry
1. Ensure that no accesses are pending or active.
2. Program the CMDCODE field of the relevant manual command register to 0001.
This ensures that all banks are idle by executing a precharge all command.
3. Wait two clock cycles.
4. Program the CMDCODE field of the relevant manual command register to 0000.
This executes a NOP command.
5. Program the CMDCODE field of the relevant manual command register to 1000.
This sets CKE low.
6. Maintain the clock at a stable value.
SDR Mechanism/Power-Down Mode Exit
1. Provide clock.
2. Program the CMDCODE field of the relevant manual command register to 0111.
This sets the relevant CKE high.
3. Program the CMDCODE field of the relevant manual command register to 0000.
This executes a NOP command.
4. Program the CMDCODE field of the relevant manual command register to 0001.
This ensures that all banks are idle by executing a precharge.
The length of time the SDRC spends in power-down mode must not exceed the refresh period; otherwise,
data becomes corrupted.
For a DDR, the sequence is as follows:
DDR Mechanism/Power-Down Mode Entry
1. Ensure that no access is currently pending or active.
2. To reduce power consumption (not mandatory): disable DLL by setting the ENADLL field of the
relevant SDRC.
register to 0x0.
3. Program the CMDCODE field of the relevant manual command register to 0001.
This ensures that all banks are idle by executing a precharge all command.
4. Program the CMDCODE field of the relevant manual command register to 0000.
This executes a NOP command.
5. Program the CMDCODE field of the relevant manual command register to 1000.
This sets the relevant CKE low.
6. Maintain the clock at a stable value.
DDR Mechanism/Power-Down Mode Exit
1. Provide clock.
2. Program the CMDCODE field of the relevant manual command register to 0111.
This sets the relevant CKE high.
3. Program the CMDCODE field of the relevant manual command register to 0000.
This executes a NOP command.
2275
SWPU177N – December 2009 – Revised November 2010
Memory Subsystem
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