Section 17 Power-Down Mode
Rev.1.00 Dec. 13, 2005 Page 650 of 1286
REJ09B0158-0100
17.6
DDR-SDRAM Power Supply Backup
17.6.1 Self-Refresh
and
Initialization
To preserve the contents of the DDR-SDRAM with battery backup, make sure that the DDR-
SDRAM is in the self-refresh mode before turning off the system power supply. When the system
power supply is turned on, whether initialization of the DDR-SDRAM and cancellation of the self-
refresh mode is needed will depend on whether the DDR-SDRAM has been in self-refresh mode
or has not been initialized. Both a transition to and a cancellation of the self-refresh mode are done
for the DDR-SDRAM by a command.
RMODE Bit: Bit 33 in MIM. The initial value is 0. Setting this bit to 1 after setting the DRE bit
in MIM to 1 causes the DDRIF to start the sequence for a transition to the self-refresh mode. For
details, see section 12.5.5 (1), Self-Refresh Mode.
SMS Bits: Bits 2 to 0 in SCR. SMS = B'011. These bits are used to assert the CKE signal (high)
and to cancel the self-refresh mode with the DESL command.
BKPRST
Signal: To prevent the CKE signal from being unstable when turning on or off the LSI
power supply, the BKPRST signal must be driven to low in synchronization with turning the LSI
power supply on or off. The
BKPRST
signal must be kept low while the system power supply is
turned off.
Transition to self-refresh
mode completed
System power
supply
turned off
System power
supply
turned on
Power-on
reset
canceled
CKE asserted
by SMS bits in SCR
Delay time of
LSI internal reset
PRESET
DDRIF reset
VDD, VDDQ
(1.25 V, 3.3 V)
CKE
min 1 ms
BKPRST
min 0 ms
min 0 ms
Figure 17.1 DDR-SDRAM Interface Operation when
Turning System Power Supply On/Off
Содержание SH7780 Series
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