r8a77850anbg Renesas Electronics Corporation., r8a77850anbg Datasheet - Page 578

• Manufacturer Part Number: r8a77850anbg
• Description: Renesas 32-bit Risc Microcomputer Superh? Risc Engine Family
• Manufacturer: Renesas Electronics Corporation.

12. DDR2-SDRAM Interface (DBSC2)
MCKE to high level, upon power-on reset the data within the SDRAM is destroyed. Hence if the
state signal is not set in advance to a state other than power supply backup state, there is the
danger that the destroyed data may be treated as the correct data.)
In this way, procedures are used to make a transition to and cancel SDRAM power supply backup
mode; if these procedures are not followed, the data in the SDRAM may be destroyed.
These procedures are explained below.
(1)
The following method is used.
1. Confirm that the controller is not being accessed. The time required for transition must not
2. Set the ACEN bit in the SDRAM operation enable register (DBEN) to 0 (access disabled).
3. Set the ARFEN bit in the SDRAM refresh control register 0 (DBRFCNT0) to 0 (automatic
4. Use the CMD bits in the SDRAM command control register (DBCMDCNT) to issue a PALL
5. Use the CMD bits in DBCMDCNT to issue a REF (auto-refresh) command.
6. Set the SRFEN bit in DBRFCNT0 to 1, to make a transition to self-refresh.
7. Check that the SRFEN bit is 1 by reading the SDRAM refresh control register (DBRFCNT0).
8. Use a general-purpose port or other means to convey to the external device that the SDRAM
9. Turn off the unnecessary power, other than the DBSC2 1.8 V I/O.
(2)
The following method is used.
1. Turn on the power supply to the LSI.
2. Input a power-on reset to the LSI.
3. After release of power-on reset, an external device should change the MBKPRST signal from
4. An external control circuit decides, using a general-use port or the like, whether to perform a
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exceed the auto-refresh interval requested by the SDRAM by interrupts or some other causes.
issue of auto-refresh disabled).
(precharge all banks) command.
has entered the self-refresh state. Upon receiving this notification, the external device should
change the MBKPRST signal from high level to low level.
low to high level.
normal initialization sequence of the SDRAM, or to recover from power supply backup mode.
For normal initialization sequence of the SDRAM, refer to section 12.5.3, Initialization
Sequence.
Transition to SDRAM Power Supply Backup Mode
Recovery from SDRAM Power Supply Backup Mode