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参数资料
| 型号： | 256MBDDRSDRAM |
| 厂商： | SAMSUNG SEMICONDUCTOR CO. LTD. |
| 英文描述： | DDR SDRAM Specification Version 0.3 |
| 中文描述： | DDR SDRAM的规格版本0.3 |
| 文件页数： | 14/51页 |
| 文件大小： | 658K |
| 代理商： | 256MBDDRSDRAM |
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REV. 0.3 November 2. 2000
256Mb DDR SDRAM
Preliminary
3.2.2 Mode Register Definition
3.2.2.1 Mode Register Set(MRS)
Figure 5. Mode Register Set
The mode register stores the data for controlling the various operating modes of DDR SDRAM. It programs
CAS latency, addressing mode, burst length, test mode, DLL reset and various vendor specific options to make
DDR SDRAM useful for variety of different applications. The default value of the mode register is not defined,
therefore the mode register must be written after EMRS setting for proper DDR SDRAM operation. The mode
register is written by asserting low on CS, RAS, CAS, WE and BA0(The DDR SDRAM should be in all bank pre-
charge with CKE already high prior to writing into the mode register). The states of address pins A0 ~ A12 in
the same cycle as CS, RAS, CAS, WE and BA0 going low are written in the mode register. Two clock cycles
are requested to complete the write operation in the mode register. The mode register contents can be
changed using the same command and clock cycle requirements during operation as long as all banks are in
the idle state. The mode register is divided into various fields depending on functionality. The burst length uses
A0 ~ A2, addressing mode uses A3, CAS latency(read latency from column address) uses A4 ~ A6. A7 is used
for test mode. A8 is used for DLL reset. A7 must be set to low for normal MRS operation. Refer to the table for
specific codes for various burst lengths, addressing modes and CAS latencies.
Address Bus
CAS Latency
A
6
0
0
0
0
1
1
1
1
A
5
0
0
1
1
0
0
1
1
A
4
0
1
0
1
0
1
0
1
Latency
Reserve
Reserve
2
(3)
Reserve
(1.5)
2.5
Reserve
Burst Length
A
2
A
1
A
0
Latency
Sequential
Reserve
2
4
8
Reserve
Reserve
Reserve
Reserve
Interleave
Reserve
2
4
8
Reserve
Reserve
Reserve
Reserve
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
A
7
0
1
mode
Normal
Test
A
3
0
1
Burst Type
Sequential
Interleave
* RFU(Reserved for future use)
should stay "0" during MRS
cycle.
A
8
0
1
DLL Reset
No
Yes
Mode Register
BA
1
BA
0
A
11
A
10
A
9
A
8
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
RFU
TM
CAS Latency
BT
Burst Length
RFU
DLL
0
BA
0
0
1
A
n
~ A
0
(Existing)MRS Cycle
Extended Funtions(EMRS)
A
12
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