LSI Logic Confidential
SDRAM Refresh
13-9
Copyright © 2001, 2002 by LSI Logic Corporation. All rights reserved.
SDRAM Mode Register
The Mode register is written by asserting RAS, CAS, and WE strobes on
the rising edge of clock (refer to specific DRAM timing specs for more
details). The 12 bits of data are written via the Address bus. Values for
the DRAM Mode register used by the DMN-8600 processor will be as
follows:
Reserved
[11:8]
Test mode
7
These test enable bits will always be written to 00000,
disabling test mode.
CAS Latency
[6:4]
The CAS latency field will be set to 2 or 3 clocks for SDR,
while for DDR it will be set to 2.5 or 3 clocks as
determined by the CAS latency field (CAS) in the Exter-
nal DRAM Configuration register (as loaded from the
serial ROM).
Burst Type
3
The Burst type field will be set to ‘0’, denoting Sequential
accesses (rather than Interleaved accesses between
banks).
Burst Length
[2:0]
The Burst length field will be assigned a value of 011,
denoting a burst length of eight. DoMiNo will terminate
bursts by issuing another read, write or stop burst
command. Bursts are needed to allow the precharge and
RAS for the second bank to be issued while transferring
from the first bank.
13.5 SDRAM Refresh
Since all MPEG applications will require DRAMs that remain active, the
DMN-8600 processor will employ Autorefresh in it’s design. Autorefresh
is enabled by driving CS, RAS, and CAS active and WE inactive on a
11
8
7
6
4
3
2
0
Reserved
Test mode
CAS Latency
Burst type
Burst length