AS4C256M16D3
Mode Register MR0
The mode-register MR0 stores data for controlling various operating modes of DDR3 SDRAM. It controls burst
length, read burst type, CAS latency, test mode, DLL reset, WR, and DLL control for precharge Power-Down,
which include various vendor specific options to make DDR3 DRAM useful for various applications. The mode
register is written by asserting low on CS#, RAS#, CAS#, WE#, BA0, BA1, and BA2, while controlling the states of
address pins according to the following figure.
Table 4. Mode Register Bitmap
BA2 BA1 BA0 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Address Field
0*1
0
0
0*1 0*1 PPD
WR
DLL TM
CAS Latency RBT 0*1
BL
Mode Register (0)
BA1 BA0 MRS mode
A7 Mode
A3 Read Burst Type
0 Nibble Sequential
A1 A0
BL
8 (Fixed)
0
0
1
1
0
1
0
1
MR0
MR1
MR2
MR3
0
1
Normal
Test
0
0
1
1
0
1
0
1
BC4 or 8 (on the fly)
BC4 (Fixed)
Reserved
1
Interleave
A11 A10 A9
WR (cycles)
Reserved
A6 A5 A4
CAS Latency
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
5*2
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Reserved
6*2
5
6
7*2
8*2
7
10*2
12*2
14*2
8
9
10
11
A12 DLL Control for Precharge PD
0
1
Slow exit (DLL off)
Fast exit (DLL on)
DLL Reset
No
A8
0
1
Yes
Note 1:
Note 2:
Reserved for future use and must be set to 0 when programming the MR.
WR (write recovery for autoprecharge) min in clock cycles is calculated by dividing tWR (ns) by tCK (ns) and
rounding up to the next integer WRmin [cycles] =Roundup (tWR / tCK). The value in the mode register must be
programmed to be equal or larger than WRmin. The programmed WR value is used with tRP to determine
tDAL.
Confidential
14
Rev. 3.0
Aug. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
