Datasheet

z Mode Register Set(MRS)
The mode register stores the data for controlling the various operating modes of DDR2 SDRAM. It controls CAS
latency, burst length, burst sequence, test mode, DLL reset, WR, and various vendor specific options to make
DDR2 SDRAM useful for various applications.The default value of the mode register is not defined, therefore
the mode register must be programmed during initialization for proper operation. The mode register is written by
asserting LOW on CS#, RAS#, CAS#, WE#, BA0 and BA1, while controlling the state of address pins A0 - A12.
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 (t
MRD
) 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 bank are in the precharge state.The mode register is
divided into various fields depending on functionality.
- Burst Length Field (A2, A1, A0)
This field specifies the data length of column access and selects the Burst Length.
- Addressing Mode Select Field (A3)
The Addressing Mode can be Interleave Mode or Sequential Mode. Both Sequential Mode and Interleave
Mode support burst length of 4 and 8.
-CAS Latency Field (A6, A5, A4)
This field specifies the number of clock cycles from the assertion of the Read command to the first read
data. The minimum whole value of CAS Latency depends on the frequency of CK. The minimum whole
value satisfying the following formula must be programmed into this field. t
CAC
(min)
≦
CAS Latency X t
CK
- Test Mode field: A7; DLL Reset Mode field: A8
These two bits must be programmed to "00" in normal operation.
- (BA0, BA1): Bank addresses to define MRS selection.
Table 5. Mode Register Bitmap
BA1 BA0 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Address Field
0
0
PD
WR
DLL
TM
C
AS Latency
BT
Burst Length
Mode Register
A8 DLL Reset A7 Mode A3 Burst Type A2 A1 A0 BL
0 No 0 Normal 0 Sequential 0 1 0 4
1 Yes 1 Test 1 Interleave 0 1 1 8
Note 1:
.For DDR2-667/800/1066, WR (write recovery for autoprecharge) min is determined by t
CK
(avg) max and WR max is
determined by t
CK
(avg) min. WR [cycles] = RU {t
WR
[ns]/t
CK
(avg)[ns]}, where RU stands for round up. The mode register
must be programmed to this value.This is also used with t
RP
to determine t
DAL
.
A12 Active power down exit time Write recovery for autoprecharge
*1
0 Fast exit (use t
XARD
) A11 A10 A9 WR(cycles) A6 A5 A4 CAS Latency
1 Slow exit (use t
XARDS
) 0 0 0 Reserved 0 0 0 Reserved
0 0 1 2 0 0 1 Reserved
BA1 BA0 MRS Mode 0 1 0 3 0 1 0 Reserved
0 0 MR 0 1 1 4 0 1 1 3
0 1 EMR(1) 1 0 0 5 1 0 0 4
1 0 EMR(2) 1 0 1 6 1 0 1 5
1 1 EMR(3) 1 1 0 7 1 1 0 6
1 1 1 8 1 1 1 7
AS4C32M16D2A-25BIN
Alliance Memory Inc.
511 Taylor Way, San Carlos, CA 94070 TEL: [phone] FAX: [phone]
Alliance Memory Inc. reserves the right to change products or specification without notice
Rev.1.2
9
Jun./2014