W9751G8JB Datasheet, PDF (10/86 Pages) Winbond – 16M  4 BANKS  8 BIT DDR2 SDRAM

W9751G8JB
Notes:
1. To guarantee ODT off, VREF must be valid and a LOW level must be applied to the ODT pin.
2. VREF must be within ±300 mV with respect to VDDQ/2 during supply ramp time.
3. VDD/VDDL voltage ramp time must be no greater than 200 mS from when VDD ramps from 300 mV to VDD min.
4. The VDDQ voltage ramp time from when VDD min is achieved on VDD to when VDDQ min is achieved on VDDQ must be
no greater than 500 mS.
tCH tCL
CLK
CLK
tIS
CKE
tIS
ODT
Command
NOP
PRE
ALL
EMRS
MRS
PRE
ALL
REF
REF
MRS
EMRS
EMRS
ANY
CMD
400nS
tRP
tMRD
tMRD
tRP
DLL
Enable
DLL
Reset
tRFC
tRFC
min 200 Cycle
tMRD
Follow OCD
Flow chart
OCD
Default
tOIT
OCD
CAL. Mode
Exit
Figure 1 – Initialization sequence after power-up
7.2 Mode Register and Extended Mode Registers Operation
For application flexibility, burst length, burst type, CAS Latency, DLL reset function, write recovery
time (WR) are user defined variables and must be programmed with a Mode Register Set (MRS)
command. Additionally, DLL disable function, driver impedance, additive CAS Latency, ODT (On Die
Termination), single-ended strobe and OCD (off chip driver impedance adjustment) are also user
defined variables and must be programmed with an Extended Mode Register Set (EMRS) command.
Contents of the Mode Register (MR) or Extended Mode Registers EMR (1), EMR (2) and EMR (3) can
be altered by re-executing the MRS or EMRS Commands. Even if the user chooses to modify only a
subset of the MR or EMR (1), EMR (2) and EMR (3) variables, all variables within the addressed
register must be redefined when the MRS or EMRS commands are issued.
MRS, EMRS and Reset DLL do not affect array contents, which mean re-initialization including those
can be executed at any time after power-up without affecting array contents.
7.2.1 Mode Register Set Command (MRS)
( CS = "L", RAS = "L", CAS = "L", WE = "L", BA0 = "L", BA1 = "L", A0 to A13 = Register Data)
The mode register stores the data for controlling the various operating modes of DDR2 SDRAM. It
programs CAS Latency, burst length, burst sequence, test mode, DLL reset, Write Recovery (WR) and
various vendor specific options to make DDR2 SDRAM useful for various applications. The default
value in the Mode Register after power-up is not defined, therefore the Mode Register must be
programmed during initialization for proper operation.
The DDR2 SDRAM should be in all bank precharge state with CKE already HIGH prior to writing into
the mode register. The mode register set command cycle time (tMRD) is required to complete the write
operation to the mode register. The mode register contents can be changed using the same command
and clock cycle requirements during normal operation as long as all banks are in the precharge state.
The mode register is divided into various fields depending on functionality. Burst length is defined by
A[2:0] with options of 4 and 8 bit burst lengths. The burst length decodes are compatible with DDR
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Publication Release Date: Oct. 12, 2010
Revision A01