r8a77850anbg Renesas Electronics Corporation., r8a77850anbg Datasheet - Page 548
r8a77850anbg
Manufacturer Part Number
r8a77850anbg
Description
Renesas 32-bit Risc Microcomputer Superh? Risc Engine Family
Manufacturer
Renesas Electronics Corporation.
Datasheet
1.R8A77850ANBG.pdf
(1692 pages)
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12. DDR2-SDRAM Interface (DBSC2)
Because access is disabled in self-refresh mode, any attempt to access data in the DDR2-SDRAM
will be ignored.
The following procedure is used to make a transition to self-refresh mode.
1. Check to make sure the DBSC2 is not being accessed. The time required for transition to self-
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 the
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.
Use the following procedure to cancel self-refresh mode.
1. Make sure that the processing described in items 2 through 6 will not be disrupted by
2. Set the SRFEN bit in DBRFCNT0 to 0, to cancel self-refresh mode.
3. Use the software to wait until access to the SDRAM is enabled. The value for this time period
4. Use the CMD bits DBCMDCNT to issue the REF (auto-refresh) command.
5. Set the ACEN bit in DBEN to 1 (access enabled).
6. Set the ARFEN bit in DBRFCNT0 to 1 (automatic issue of auto-refresh enabled). Normal
(2)
Shifting to self-refresh mode is done by writing 1 to the self-refresh enable bit (SRFEN) in the
SDRAM refresh control register 0 (DBRFCNT0). Self-refresh mode can be cancelled by writing 0
to the SRFE bit.
Because access is disabled in self-refresh mode, no commands are issued to the SDRAM if an
attempt to access data in the SDRAM is made.
The following procedure is used to make a transition to self-refresh mode.
Rev.1.00 Jan. 10, 2008 Page 518 of 1658
REJ09B0261-0100
refresh must not exceed the auto-refresh interval requested by the SDRAM by interrupts or
some other causes.
issue of auto-refresh disabled).
PALL (precharge all banks) command.
interrupts, etc. to assure the auto-refresh interval.
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.
access is enabled after that point).
Self-Refreshing (Stopping the Clock or Changing the Frequency)
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