Section 17 Power-Down Mode
Rev.1.00 Dec. 13, 2005 Page 651 of 1286
REJ09B0158-0100
17.6.2
DDR-SDRAM Backup Sequence when Turning Off System Power Supply
The sequence when the system power supply is turned off is shown below.
Figure 17.1 shows the sequence of a transition to the self-refresh mode to turn off the system
power supply.
(A) Confirm that all transactions of the DDRIF by on-chip peripheral modules are completed.
(B) Issue the all bank precharge command (PREALL) with bits SMS2 to SMS0 in SCR by
software. Activated banks will be closed. After that, issue the auto-refresh command (REFA)
with bits SMS in SCR to perform refresh on all rows.
(C) Specify the DRE and RMODE bits in MIM of the DDRIF to put the SDRAM into the self-
refresh mode. At this time, keep the DCE bit set to 1. The self-refresh command will be
automatically issued and the CKE signal will be driven to low by the DDRIF. After that, the
DDR-SDRAM will automatically enter the power-down mode.
(D) The SELFS bit in MIM is set to 1.
(E) Drive the
BKPRST
signal from high to low. Immediately after the system power supply is
turned off, the CKE output may be unstable. Before turning off the system power supply, use
the external
BKPRST
signal to keep the CKE signal input of the DDR-SDRAM low until
canceling the power-on reset as shown in figure 17.1.
(F) Turn off the system power supply (1.25 V and 3.3 V).
Note that in the transition from auto-refresh state to self-refresh state, the current auto-refresh
state should have been finished or been disabled before the transition.
After the system power supply is turned on, the CKE output may remain unstable until the
clock is supplied after the LSI power supply has become stable. Use the external
BKPRST
signal to keep the CKE signal input of the DDR-SDRAM low until canceling the power-on
reset as shown in figure 17.1.
Содержание SH7780 Series
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