LSI Logic Confidential
13-8
SDRAM Interface
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
RAS time for the last three banks are hidden behind the first bank
access. Larger transfers are sustained without bubbles using 4 banks by
closing active banks as new banks are opened.
To overlap across accesses without overhead (hide precharge of old
pages and activate of future pages) in memory configurations with at
least 8 banks, the first 4 banks of the next access may be activated
before closing the last 4 banks of the previous access.
13.4 SDRAM Initialization
DRAMs require an initialization sequence to be performed when the
DMN-8600 is reset through the reset pin or the host control register.
Note:
Proper initialization assumes that the SDRAM Clock
Control and External SDRAM Configuration register have
been programmed, and that the controller has been taken
out of Stop mode by programming the Internal Clock
Control register (see
After reset, CS and SDRAM_DQM will be held high, and CKE will be low.
Once the above registers are programmed, the DMN-8600 will initialize
the DRAM using the following sequence:
•
For SDR: Two precharge-all-banks commands are issued, followed
by two refresh commands before the mode register is programmed
for normal operation.
•
For DDR: One precharge-all-banks command is issued, followed by
an extended mode register (EMRS) write to enable the DLL. Then
the mode register is programmed to reset the DLL. After a delay of
at least 200 cycles, another precharge-all-banks command is issued,
then at least two refresh commands are issued, followed by the
mode register write to prepare the DRAM for normal operation.
The DRAM chips are configured via an internal Mode register, a 12-bit
register that defines Burst length, access type, and CAS latency, as well
as some vendor-specific test fields. The mode register is written during
the reset sequence. A bit assignment of the register is shown in
Содержание DMN-8600
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