AS4C512M8D3
Register Definition
Programming the Mode Registers
For application flexibility, various functions, features, and modes are programmable in four Mode Registers, provided
by the DDR3 SDRAM, as user defined variables and they must be programmed via a Mode Register Set (MRS)
command. As the default values of the Mode Registers are not defined, contents of Mode Registers must be fully
initialized and/or re-initialized, i.e., written, after power up and/or reset for proper operation. Also the contents of the
Mode Registers can be altered by re-executing the MRS command during normal operation. When programming the
mode registers, even if the user chooses to modify only a sub-set of the MRS fields, all address fields within the
accessed mode register must be redefined when the MRS command is issued. MRS command and DLL Reset do
not affect array contents, which mean these commands can be executed any time after power-up without affecting
the array contents.
The mode register set command cycle time, tMRD is required to complete the write operation to the mode register
and is the minimum time required between two MRS commands shown in Figure of tMRD timing.
Figure 6. tMRD timing
T0
T1
T2
Ta0
Ta1
Tb0
Tb1
Tb2
Tc0
Tc1
Tc2
CK#
CK
NOP/DES
VALID
NOP/DES
VALID
NOP/DES
VALID
NOP/DES
VALID
VALID
VALID
VALID
VALID
VALID
VALID
MRS
MRS
VALID
VALID
VALID
VALID
COMMAND
ADDRESS
VALID
VALID
CKE
Old Settings
Updating Settings
New Settings
Settings
tMRD
tMOD
RTT_Nom ENABLED prior and/or after MRS command
ODTLoff + 1
VALID
VALID
VALID
VALID
ODT
ODT
RTT_Nom DISABLED prior and after MRS command
VALID VALID VALID
VALID
VALID
VALID
VALID
VALID
VALID
VALID
TIME BREAK
Don't Care
Confidential
12
Rev. 3.0
Aug. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
