Renesas SH7781 - Manual (Page 549)

12. DDR2-SDRAM Interface (DBSC2)
Rev.1.00 Jan. 10, 2008 Page 519 of 1658
REJ09B0261-0100
1. Check to make sure the DBSC2 is not being accessed. The time required for transition to self-
refresh must not exceed the auto-refresh interval requested by the SDRAM by interrupts or
some other causes.
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
issue of auto-refresh disabled).
4. Use the CMD bits in the SDRAM command control register (DBCMDCNT) to issue the
PALL (precharge all banks) command.
5. Use the CMD bits in DBCMDCNT to issue the REF (auto-refresh) command.
6. Set the SRFEN bit in DBRFCNT0 to 1 to make a transition to self-refresh mode.
7. Read DBRFCNT0, and make sure the SRFEN bit is set to 1.
8. Using the CPG setting, stop the clock to the DBSC2, or change the frequency.
Use the following procedure to cancel self-refresh mode.
1. Re-start the clock supply, and wait until the clock is being stably supplied to the DBSC2.
2. Writing to the DDRPAD frequency setting register (DBFREQ) enters the DLL settings.
A. Set DLLRST = 0.
B. Set the DDRPAD frequency in the FREQ bit.
C. After DLLRST = 1 has been set, use the software to wait the time necessary for the DLL to
stabilize with the DDRPAD, which is at least 100
μs.
3. Set the SRFEN bit in DBRFCNT0 to 0, to cancel self-refresh mode.
4. Use the software to wait until access to the DDR2-SDRAM is enabled. The value for this time
period must be at least as long as the time until the non-read command is issued following
cancellation of the self-refresh status (tXSNR time) that is specified in the datasheet for the
SDRAM being used.
5. Use the CMD bits in DBCMDCNT to issue the REF (auto-refresh) command.
6. Set the ACEN bit in DBEN to 1 (access enabled).
7. Set the ARFEN bit in DBRFCNT0 to 1 (automatic issue of auto-refresh enabled). Normal
access is enabled after that point.