BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
126
Section 6: DRAM
Document
1250_1125-UM100CB-R
SDRAM R
EFRESH
The memory controller uses the SDRAM auto-refresh command to refresh the memory during normal
operation. The refresh interval for a channel is set (in memory clocks) in the
mc_clock_cfg
register. In parts
where the system_revision indicates PERIPH_REV3 or later this register also has fields to completely disable
refresh (useful only during debugging, to avoid the scope being triggered by refresh cycles) or disable refresh
for particular (i.e. unused) chip selects.
Software can cause Auto Refresh commands to be sent to the SDRAM as described in
Initialization and Commands” on page 126
. This has no effect on the refresh interval counter.
SDRAM I
NITIALIZATION
AND
C
OMMANDS
The DDR SDRAMs accept a number of commands that are not used as part of regular operation. These can
be issued under software control by writing the
mc_dramcmd
register with the command to be performed and
the chip selects that should be asserted when the command is executed. The memory controller will insert a
synchronization point before the command is executed so that all buffers are empty. In some cases the
commands require additional data encoded in the address lines. The
mc_drammode
register holds the data
to be encoded (on address lines A[11:0] for standard DDR parts and A[14:0] for FCRAMs).
Table 69: Commands that can be Issued Through mc_dramcmd Register
Name
Command
Description
EMRS
Write Extended Mode Register
Write the value in the mc_drammode register to the Extended Mode Register
in the selected parts.
MRS
Write Mode Register
Write the value in the mc_drammode register to the Mode Register in the
selected parts.
PRE
Precharge all banks
Issue a precharge command to the SDRAMs with address bit 10 high to
cause all banks to be precharged. If the pre_on_8 bit is set then this
command will run the precharge command with address bit 8 high.
AR
Auto Refresh
Issue an Auto Refresh command to the SDRAMs.
SREF_set
Enter Self Refresh mode
Set the SDRAM into Self Refresh mode by issuing a Self Refresh command
and deasserting CKE then stopping the clock.
SREF_clr
Exit Self Refresh mode
Remove the SDRAM from Self Refresh mode by starting the clock, asserting
CKE and issuing NOP commands to the part. Software must ensure that the
memory is not accessed for the required time after the part is removed from
Self Refresh mode (normally 200 memory clocks).
PDN_set
Enter Power Down mode
Set the SDRAM into Power Down mode by issuing a NOP command and
deasserting CKE.
PDN_clr
Exit Power Down mode
Remove the SDRAM from Power Down mode by asserting CKE and issuing
NOP commands to the part. Software must ensure that the memory is not
accessed for the required time after the part is removed from Power Down.